United States v. Mulkern ( 2022 )


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  •           United States Court of Appeals
    For the First Circuit
    No. 21-1475
    UNITED STATES,
    Appellee,
    v.
    SEAN MULKERN,
    Defendant, Appellant.
    APPEAL FROM THE UNITED STATES DISTRICT COURT
    FOR THE DISTRICT OF MAINE
    [Hon. Jon D. Levy, U.S. District Judge]
    Before
    Barron, Chief Judge,
    Selya and Kayatta, Circuit Judges.
    John W. VanLonkhuyzen and Verrill Dana LLP on brief for
    appellant.
    Darcie N. McElwee, United States Attorney, and Noah Falk,
    Assistant United States Attorney, on brief for appellee.
    September 27, 2022
    KAYATTA, Circuit Judge. This case arises from a parking-
    lot   confrontation   following   a    road-rage   incident    between   the
    driver of a white Corvette and several men in a landscaping truck.
    Reports of that confrontation led law enforcement to stop Sean
    Mulkern in his white Corvette the next day.              The subsequent
    searches of Mulkern's vehicle and motor home yielded evidence
    supporting drug-trafficking and firearms charges.             Mulkern moved
    to suppress all of the evidence derived from what he argues were
    illegal searches of his person and vehicles.          After the district
    court denied that motion in relevant part, Mulkern pleaded guilty.
    At sentencing, the district court found that Mulkern had three
    prior qualifying offenses that rendered him subject to a mandatory
    minimum sentence under the Armed Career Criminal Act (ACCA), 
    18 U.S.C. § 924
    (e).   Mulkern claims on appeal that the district court
    erred first in denying his suppression motion and second in finding
    him eligible for the ACCA sentence.        As we explain below, we see
    no error on either score, so we affirm Mulkern's conviction and
    sentence.
    I.
    A.
    The facts giving rise to this case unfolded over two
    days in May 2017.       We recite those facts "in the light most
    favorable to the district court's ruling" denying Mulkern's motion
    to suppress, though we note Mulkern's "contrary view of the
    - 2 -
    testimony presented at the suppression hearing" where relevant.
    United States v. Sierra-Ayala, 
    39 F.4th 1
    , 6 (1st Cir. 2022)
    (quoting United States v. Rodríguez-Pacheco, 
    948 F.3d 1
    , 3 (1st
    Cir. 2020)).
    1.
    On May 24, 2017, Officers Warren Day and Jessica Ramsay
    of the Buxton, Maine police department responded to a dispatch
    call   reporting    a   possible     road-rage   incident   and   armed
    confrontation. As relayed by the dispatcher, a man driving a white
    Corvette with red rims had reportedly pulled a gun on a man at the
    Timberline Country Store in Buxton. The dispatcher relayed a Maine
    license plate number reported for the Corvette, "2512VW," but noted
    that this number was actually registered to a black Lexus, rather
    than a white Corvette.
    While en route to the Timberline, Officer Day spoke on
    the phone with one of the reported victims, Scott Wallingford.
    Wallingford, who had by that time left the Timberline and was on
    his way to a job site, confirmed that the driver of a white Corvette
    had displayed a gun and threatened him and his companions.
    When Officers Day and Ramsay arrived at the Timberline,
    the Corvette was no longer present.        The officers spoke with two
    store employees, who showed the officers a security video of the
    confrontation.     According to Officer Ramsay's testimony at the
    suppression hearing, the video depicted a white Corvette and a
    - 3 -
    landscaping truck in the store's parking lot.                 Officer Ramsay
    described the Corvette as "very distinct."         Three occupants of the
    truck got out, approached the Corvette, and argued with its driver.
    The driver of the Corvette then "reached into the back of the
    Corvette and pulled something out -- it was difficult to tell what
    it was at the time," and then held the object against his chest.
    The three men on foot then "got elevated in their behavior";
    "[t]hey started yelling and pointing" before the Corvette drove
    off.
    One of the employees, Jaaron Thurlow, had been working
    during the incident.      He spoke with the officers after they had
    reviewed the video.      He recounted that he had seen three men in
    the parking lot arguing with a fourth man in the driver's seat of
    a white Corvette with two red stripes running from the front to
    the back.    Thurlow said that the Corvette driver was in his 50s
    and wore glasses.      He reported that the men yelled at each other
    before the Corvette drove away and that the group of remaining men
    then came into the store to talk to him.          As related by Thurlow,
    the group told him that the Corvette had sped by them on the road,
    that they followed him into the parking lot to confront him about
    his dangerous driving, and that the Corvette driver had then pulled
    a gun on them.
    On   the   basis   of   the   video   and   the    reports   from
    Wallingford and Thurlow, Officer Ramsay requested that her station
    - 4 -
    issue a "Caution Officer Safety" alert -- also referred to as a
    "BOLO" (short for "be on the lookout") -- in a statewide law
    enforcement system.   The BOLO read in full:
    ***     CAUTION     OFFICER    SAFETY     ***
    ON TODAY'S DATE BUXTON POLICE DEPARTMENT TOOK
    A REPORT OF A MALE IN A WHITE CORVETTE WITH
    RED RIMS WAS IN A ALTERCATION AT TIMBERLINE
    COUNTRY STORE 222 NARRAGANSETT TRAIL.     THE
    OPERATOR A MALE IN HIS 40'S WHITE SHIRT AND
    BALL CAP, PULLED OUT A HAND GUN AND SHOWED IT
    TO THE VICTIM.    THE VEHICLE WAS LAST SEEN
    HEADED TOWARD GORHAM.    IF LOCATED STOP AND
    IDENTIFY THE DRIVER.      THANK YOU FOR ANY
    ASSISTANCE.
    2.
    The next day, May 25, Patrol Sergeant Timothy Morrell of
    the nearby Westbrook, Maine police department observed a white
    Corvette with red rims, as described in the BOLO that he had seen
    come in the previous day.   He testified at the suppression hearing
    that, based on the distinctive nature of the vehicle, he thought,
    "The odds of that being someone else are pretty slim."     When the
    Corvette stopped and parked, Sergeant Morrell ran its license plate
    number -- 2513VW -- and learned that it was registered to the
    defendant, Sean Mulkern.    He was also able to see that the driver
    appeared to be a man in his 40s with a baseball cap, as described
    in the BOLO.
    He then called Buxton PD to inform them he believed he'd
    located the vehicle from their notice.         Based on the vehicle
    description and plate number, Buxton's police chief confirmed that
    - 5 -
    the sergeant had found the vehicle Buxton PD was investigating and
    that his department would send officers out to speak with the
    driver.      Sergeant Morrell acknowledged that, after the call with
    Buxton PD, he did not believe that he personally had sufficient
    information at that point to arrest Mulkern.
    In     the   meantime,    Sergeant   Morrell    ran   a   criminal
    background check on Mulkern and learned that he had been convicted
    of at least one felony and had a history of drug-trafficking
    charges.      He also identified the driver he observed as Mulkern,
    based   on    the    booking   photo   in   the   criminal   history   report.
    Sergeant Morrell then called some other local officers to assist
    with surveillance while waiting for Buxton PD.                 However, once
    Mulkern got back into the Corvette and began to drive away,
    Sergeant Morrell decided to change course and conduct a traffic
    stop because he did not want Mulkern to get away.                  As Mulkern
    pulled out of the driveway towards the direction of Sergeant
    Morrell, he saw the sergeant and then turned hard in the other
    direction.        Sergeant Morrell then activated his lights and pulled
    Mulkern over.
    Sergeant Morrell and another Westbrook officer, Sergeant
    Brian Olson, who had arrived to assist, then ordered Mulkern out
    of the car and frisked him.            Sergeant Morrell started the frisk
    but soon stopped so that he could secure the scene, letting
    Sergeant Olson conduct the frisk instead.             Sergeant Olson felt a
    - 6 -
    hypodermic needle in Mulkern's breast pocket and, when Mulkern
    reached for the needle and began to attempt to explain that it was
    his girlfriend's, the officers handcuffed him.                 Sergeant Olson
    then proceeded with the frisk and discovered a cigarette package
    in    another    pocket.     The    package's      outer   cellophane   wrapper
    contained "white crystal rocks" that the officers believed to be
    crack cocaine.
    At that point, according to Sergeant Morrell's testimony
    at    the   suppression     hearing,      the   officers   believed   they   had
    developed probable cause to search Mulkern's vehicle for evidence
    of drug trafficking.        In conducting this search, they discovered
    a backpack containing drugs, a gun, and over $13,000 in cash.
    During the course of the frisk and vehicle search, Mulkern made
    several incriminating statements:               He told the officers that the
    rocks in the cigarette package were his; spontaneously shouted out
    during the vehicle search that there was a gun in the car; and,
    when officers found the backpack, stated something to the effect
    of, "Yeah, you got it, that's it."
    Later that day, evidence derived from the traffic stop
    and    vehicle    search,    as    well    as    information   provided   by   a
    cooperating defendant, was used to obtain a search warrant for
    Mulkern's Winnebago mobile home.                Law enforcement executed the
    warrant that evening and discovered further drugs and guns in the
    Winnebago.
    - 7 -
    B.
    A grand jury indicted Mulkern on three counts of drug
    trafficking and firearms offenses.      Mulkern moved to suppress all
    physical evidence and statements obtained from the stop under
    several theories, including that the initial stop was an unlawful
    seizure, that the subsequent search of his person exceeded the
    bounds of a lawful pat-frisk, that the evidence obtained pursuant
    to the ensuing search warrant for his Winnebago was tainted by the
    earlier infirmities as so-called "fruit of the poisonous tree,"
    and, finally, that several of his statements during the traffic
    stop were the product of custodial interrogation without the
    warnings required by Miranda v. Arizona, 
    384 U.S. 436
     (1966).
    The district court agreed with Mulkern as to part of his
    Fifth Amendment Miranda claim and suppressed any statements that
    were prompted by the officers' questioning, while declining to
    suppress statements Mulkern spontaneously offered.      No challenge
    is pressed on appeal by either party to the district court's
    resolution of that claim.1
    As to the search and seizure claims, the district court
    denied Mulkern's motion.     While the court agreed that the search
    1  Mulkern does on appeal continue to seek suppression of all
    of his statements to law enforcement during the stop, though he
    does so on Fourth Amendment grounds, as the fruits of an unlawful
    search and seizure, rather than on Miranda grounds. We therefore
    consider the statements in our analysis of the Fourth Amendment
    challenge.
    - 8 -
    of Mulkern's person would have exceeded the lawful bounds of a
    pat-frisk if it could only have been justified on that basis, the
    court upheld all of the searches on an alternative basis:                   Law
    enforcement officers were justified in searching Mulkern's person
    and vehicle as a search incident to arrest because they had
    probable cause before the search to arrest Mulkern for being a
    felon in possession of a firearm.
    Following the suppression ruling, Mulkern pleaded guilty
    to counts one and three of the indictment, for, respectively:
    (1) possession of cocaine base, cocaine hydrochloride, and heroin
    with intent to distribute, in violation of 
    21 U.S.C. §§ 841
    (a)(1),
    (b)(1)(B), and (b)(1)(C); and (2) being a felon in possession of
    a firearm, in violation of 
    18 U.S.C. §§ 922
    (g)(1) and 924(a).2               He
    reserved the right to appeal the denial of his motion to suppress.
    In its presentence investigation report, U.S. Probation
    recommended that Mulkern be sentenced as an armed career criminal
    on the basis of a 1994 Maine burglary conviction (as a "violent
    felony")     and     two   2006   Maine    drug-trafficking   convictions   (as
    "serious drug offense[s]").           Mulkern disputed his eligibility for
    an ACCA sentence in briefing and at the sentencing hearing, but
    the       district     court      ultimately      agreed   with   Probation's
    2 Count Two, possession of a firearm in furtherance of a drug
    trafficking crime, was dismissed pursuant to an informal agreement
    with the government.
    - 9 -
    recommendation.3    The court varied downward from the sentencing
    range provided by the U.S. Sentencing Guidelines and sentenced
    Mulkern to ACCA's mandatory-minimum term of fifteen years of
    incarceration.
    II.
    Mulkern challenges the denial of his motion to suppress
    and his eligibility for an ACCA mandatory-minimum sentence.           We
    consider these arguments in turn.
    A.
    In reviewing a district court's denial of a motion to
    suppress, "we review legal conclusions de novo and factual findings
    for clear error."      United States v. Batista, 
    31 F.4th 820
    , 823
    (1st Cir. 2022).       While Mulkern argued for suppression under
    several   constitutional      theories    below,   including   that   his
    statements were obtained in violation of the Fifth Amendment's
    prohibition against self-incrimination, his arguments on appeal
    focus exclusively on purported Fourth Amendment violations, so we
    train our attention accordingly.
    1.
    We   begin   with    background   principles   governing    our
    assessment of Mulkern's suppression claim.         The Fourth Amendment
    3  We reserve further description of the predicate offenses
    and the sentencing proceedings for our discussion of Mulkern's
    sentencing claim.
    - 10 -
    guarantees "[t]he right of the people to be secure in their
    persons,   houses,      papers,    and   effects,   against     unreasonable
    searches and seizures."      U.S. Const. amend. IV.      Thus, a search or
    seizure by police does not offend the Fourth Amendment if that
    conduct is "reasonable."        United States v. Rasberry, 
    882 F.3d 241
    ,
    246 (1st Cir. 2018).         The set of constitutionally permissible
    seizures includes "a warrantless arrest by a law officer" when
    "there is probable cause to believe that a criminal offense has
    been or is being committed."         Devenpeck v. Alford, 
    543 U.S. 146
    ,
    152 (2004).      And, relatedly, the universe of constitutionally
    reasonable searches includes warrantless searches incident to an
    arrest, during which law enforcement may conduct "a full search of
    the person" of an arrestee.         United States v. Robinson, 
    414 U.S. 218
    , 235 (1973).      Where an arrest follows a traffic stop, officers
    may also search the arrestee's vehicle incident to the arrest "if
    the   arrestee   is    within     reaching   distance   of    the   passenger
    compartment at the time of the search or it is reasonable to
    believe the vehicle contains evidence of the offense of arrest."
    Arizona v. Gant, 
    556 U.S. 332
    , 351 (2009).
    The critical inquiry in many situations therefore trains
    on whether police possess probable cause for an arrest, which may
    then open the door to an incidental search.             Probable cause "is
    not a high bar."      Kaley v. United States, 
    571 U.S. 320
    , 338 (2014).
    "It 'requires only the kind of fair probability on which reasonable
    - 11 -
    and prudent [people,] not legal technicians, act.'"        Rasberry, 882
    F.3d at 250 (alteration in original) (quoting Kaley, 571 U.S. at
    338).
    Police have probable cause to arrest when, "acting upon
    apparently trustworthy information," they "reasonably can conclude
    that a crime has been . . . committed and that the suspect is
    implicated in its commission."        Karamanoglu v. Town of Yarmouth,
    
    15 F.4th 82
    , 87 (1st Cir. 2021) (alteration in original) (quoting
    United States v. Flores, 
    888 F.3d 537
    , 543 (1st Cir. 2018)).            For
    example, the "[u]ncorroborated testimony of a victim or other
    percipient   witness,   standing    alone,   ordinarily   can   support   a
    finding of probable cause."     
    Id.
     at 87–88 (quoting Acosta v. Ames
    Dep't Stores, Inc., 
    386 F.3d 5
    , 10 (1st Cir. 2004)).            Even where
    a witness's account is disputed, "police officers do not have an
    'unflagging duty' to complete a full investigation before making
    a probable cause determination."        
    Id. at 88
     (quoting Acosta, 
    386 F.3d at 11
    ). Nevertheless, facts which otherwise may be sufficient
    to establish probable cause can be overborne by contrary material
    facts known to law enforcement.       Cf. Jordan v. Town of Waldoboro,
    
    943 F.3d 532
    , 541–43 (1st Cir. 2019) (finding that correcting a
    misrepresentation   and   two   material     omissions    in    a   warrant
    affidavit "would have painted a fundamentally different picture"
    which "would fall short of establishing probable cause").
    - 12 -
    We   review   probable-cause    determinations   objectively,
    "asking whether the facts constitute probable cause of a crime,
    rather than whether the officer thought they did."           United States
    v. Monell, 
    801 F.3d 34
    , 40 (1st Cir. 2015); see also Devenpeck,
    
    543 U.S. at 153
     ("An arresting officer's . . . subjective reason
    for making the arrest need not be the criminal offense as to which
    the known facts provide probable cause.").
    When determining the universe of facts that we may
    properly consider as the basis for probable cause, we may look to
    "the collective knowledge of several officers."         United States v.
    Cruz-Rivera, 
    14 F.4th 32
    , 44 (1st Cir. 2021).           Specifically, we
    "look to the collective information known to the law enforcement
    officers    participating     in    the     investigation    rather   than
    isolat[ing] the information known by the individual arresting
    officer."    
    Id.
     (alteration in original) (quoting United States v.
    Azor, 
    881 F.3d 1
    , 8 (1st Cir. 2017)).
    2.
    With these principles in mind, we now take up Mulkern's
    contention that the district court erred by failing to suppress
    evidence from the traffic stop and ensuing searches.              Mulkern
    argues that the officers did not have probable cause to arrest him
    from the outset of the stop and that the search of his person
    revealing the rocks of crack cocaine exceeded the bounds of a
    lawful frisk under Terry v. Ohio, 
    392 U.S. 1
     (1968).          As a result,
    - 13 -
    he says, all evidence obtained from the traffic stop and ensuing
    searches, including the statements he made during the searches and
    interactions     with   law   enforcement,     were   obtained   unlawfully.
    Moreover, because this evidence was used to obtain the search
    warrant for the Winnebago, Mulkern argues that that evidence, too,
    must be suppressed as so-called "fruit of the poisonous tree."
    See,    e.g.,   Sierra-Ayala,   39    F.4th   at   16–19   (discussing   this
    doctrine).
    Mulkern's arguments hinge on his contention that the
    officers lacked probable cause to arrest him for being a felon in
    possession of a firearm at the time they initiated the traffic
    stop.    Cf. Batista, 31 F.4th at 823 (holding that, "if there was
    probable cause for law enforcement to believe [the defendant] was
    committing a crime when he was pulled over, there was no error in
    denying the motion to suppress" evidence obtained from a search
    during the traffic stop); Rasberry, 882 F.3d at 249 (affirming the
    lawfulness of a search, originally conceived of as a frisk, where
    the totality of circumstances gave the officer probable cause to
    make an arrest before the search).            We conclude that the police
    did have such probable cause and that Mulkern's claim accordingly
    fails.
    The district court ably explained that the basis for
    probable cause to believe Mulkern had committed a crime rested on
    three factual determinations.         First, based on the facts available
    - 14 -
    to the police, it would have been reasonable to believe the driver
    of the white Corvette on May 24 possessed a gun.              Second, it would
    have been reasonable to conclude that Mulkern was the driver of
    that Corvette on May 24.          Third, they could reasonably conclude
    that Mulkern was a felon at the time of that possession.                  Mulkern
    has    conceded    the   third   point,    presumably    based    on   Sergeant
    Morrell's    criminal-history          search   revealing     Mulkern's    felon
    status, so we discuss only the first two conclusions.
    As to the first, the primary source supporting the
    presence of a gun during the Timberline incident was Wallingford,
    in his reports to the 911 dispatcher and then to Officer Day in
    his initial telephonic interview.               The Timberline store clerk,
    Thurlow, then also told Buxton police that Wallingford and his
    companions had come into the store immediately after the Corvette
    left and told him that they had been threatened with a gun.                  And
    while Officer Ramsay could not confirm that what she saw on the
    store's surveillance video was in fact a gun, she testified that
    she did see the driver pull something from behind him and hold it
    against his chest, leading the other men to display "elevated"
    behavior towards him.
    Mulkern argues that Officer Ramsay did not definitively
    identify a gun from the video and that the witnesses may not have
    been    entirely    reliable     for    various    reasons,    including    that
    Wallingford may have himself been the aggressor in the altercation
    - 15 -
    and may have been motivated to minimize his own role.         But the law
    does not require the police to have entirely reliable information
    or absolute certainty when making a probable-cause determination
    -- only "apparently trustworthy information,"            Karamanoglu, 15
    F.4th at 87, and a "fair probability," Rasberry, 882 F.3d at 250
    (quoting Kaley, 571 U.S. at 338).          Wallingford's account of a
    brandished gun, as relayed to Officer Day over the phone, matched
    what he had earlier conveyed to Thurlow and to the 911 operator in
    his initial call.    These reports were all further corroborated by
    the video's confirmation that some object was indeed brandished.
    Objectively     viewed,   this   information     rendered   reasonable   a
    determination that the driver of the Corvette on May 24 had a gun.
    See Karamanoglu, 15 F.4th at 87–88.
    The second factual conclusion -- that Mulkern was the
    Corvette's driver on May 24 -- strikes us as even more reasonable.
    As a threshold matter, the same car clearly was involved on both
    days.   Wallingford and Thurlow described, and the security footage
    depicted, a white Corvette with distinctive features that all
    substantially    match    Mulkern's   vehicle.    The   vehicle   Sergeant
    Morrell saw the next day was fitted with a license plate number
    just one digit off of what had been recorded by the dispatcher the
    - 16 -
    prior day.4    Mulkern quibbles with some of the descriptions of the
    vehicle provided by witnesses as insufficient to associate his
    vehicle with the one at the Timberline, arguing that his rims are
    only partially red and that the stripe on his car is black, rather
    than the red striping reported by Thurlow.     But the officers were
    hardly unreasonable in concluding that it was likely the witnesses
    misapprehended those small details, rather than that there were
    two white Corvettes with red trim and virtually identical non-
    vanity plate numbers (and also a black Lexus with a duplicate of
    the plate number given on May 24).
    Mulkern does not dispute that he was the driver on May 25
    or that Sergeant Morrell accurately identified him before pulling
    him over.     That tees up the question whether Mulkern was also the
    driver on May 24.     Given that he was the registered owner of the
    white Corvette, that he was driving the car in a neighboring town
    the next day, and that there was no reason to think that he let
    another man his approximate age in a ball cap drive his Corvette
    on May 24, the police could reasonably conclude as part of their
    probable-cause determination that Mulkern was indeed the driver on
    both days.     Cf. Kansas v. Glover, 
    140 S. Ct. 1183
    , 1188, 1191
    4  Buxton Officer Ramsay testified at the suppression hearing
    that, based on subsequent interviews with the victim-witnesses
    from the Timberline, she believed the witnesses likely reported
    the correct number -- 2513VW -- and that the number "g[ot] lost in
    translation at some point," causing dispatch to "just change[] one
    number of that plate" to 2512VW.
    - 17 -
    (2020) (knowledge that a person is the registered owner of a
    particular pickup truck, absent other information, gives rise to
    "an entirely reasonable inference" that the truck's driver is its
    owner, even if the owner's license is revoked).
    To tie up a final loose end, it matters not that Sergeant
    Morrell   did   not   subjectively   believe   that   he   personally   had
    sufficient information to support probable cause to arrest Mulkern
    when the officers initiated the search.        As we have explained, our
    review of probable cause determinations is an objective inquiry,
    unconcerned with the actual beliefs and motivations of the officers
    on the scene.    See Monell, 801 F.3d at 40; see also United States
    v. Guerrero, 
    19 F.4th 547
    , 553–59 (1st Cir. 2021) (surveying
    Supreme Court and circuit precedent reiterating the objectivity of
    Fourth Amendment inquiries).
    We therefore agree with the district court that the
    Buxton and Westbrook police departments collectively possessed
    sufficient information to reasonably conclude: (1) that the driver
    of the white Corvette at the Timberline possessed a gun; (2) that
    Sean Mulkern was that driver on May 24, 2017; and (3) that Mulkern
    was at the time a convicted felon.         These conclusions provided
    police with probable cause to arrest Mulkern for being a felon in
    possession of a firearm, with the result that they could lawfully
    search his person incident to an arrest.       That search of Mulkern's
    person, if incident to an arrest, would also lawfully extend to
    - 18 -
    any search of the cigarette package containing the crack cocaine.
    See Robinson, 
    414 U.S. at
    235–36 ("Having in the course of a lawful
    search come upon the crumpled package of cigarettes, [the officer]
    was entitled to inspect it; and when his inspection revealed the
    heroin capsules, he was entitled to seize them."). Under the facts
    of this case, that search incident to arrest could also permissibly
    include a search of his vehicle, as police could search for
    evidence of the crime of arrest -- namely, the gun reportedly seen
    in the car the day before.     See Gant, 
    556 U.S. at 351
    .     And,
    needless to say, if the evidence recovered from the traffic stop
    was lawfully obtained, then there was no constitutional infirmity
    in using that evidence to obtain the search warrant for the
    Winnebago.   There was therefore no error in the district court's
    decision denying Mulkern's motion to suppress.
    B.
    We turn next to Mulkern's argument that he was improperly
    sentenced under ACCA.   As we explain further below, close review
    of the sentencing record compels us to find that Mulkern waived
    the specific argument he now raises.    "[A] party waives a right
    when he intentionally relinquishes or abandons it."   United States
    v. Orsini, 
    907 F.3d 115
    , 119 (1st Cir. 2018) (quoting United States
    v. Rodriguez, 
    311 F.3d 435
    , 437 (1st Cir. 2002)).   It follows that
    when a litigant "explicitly affirms a fact in the district court,
    that party risks waiving" his right to argue that the fact was
    - 19 -
    insufficiently established.        
    Id.
     (quoting United States v. Bauzó-
    Santiago, 
    867 F.3d 13
    , 24 (1st Cir. 2017)).           "As a general rule,
    a waived claim is unreviewable and, thus, cannot be revisited on
    appeal."    
    Id.
    Of the three state convictions supporting the district
    court's    ACCA   finding,   Mulkern   challenges    on   appeal   only    the
    classification of his two Maine drug-trafficking convictions.               We
    therefore begin with some background on our treatment under ACCA
    of Maine's trafficking statutes, Me. Rev. Stat. Ann. tit. 17-A,
    §§ 1101–1103.     Those statutes classify both cocaine and heroin as
    "Schedule W" drugs, id. § 1102(1)(F), (I), and treat knowing or
    intentional    trafficking    in   Schedule W   drugs     as   unlawful,   id.
    § 1103(1-A)(A).
    To qualify as ACCA-predicate "serious drug offense[s],"
    these state-law trafficking crimes must have required proving at
    least "possessi[on] with intent to manufacture or distribute" the
    drugs.     See 
    18 U.S.C. § 924
    (e)(2)(A)(ii).        In the case of heroin
    and fentanyl, Maine's trafficking regime at the time of Mulkern's
    offenses allowed for a conviction in circumstances that do not
    necessarily involve such intent.5        See United States v. Mulkern,
    5  The provisions treating heroin and fentanyl separately from
    other drugs for trafficking purposes (formerly found at Me. Rev.
    Stat. Ann. tit. 17-A, § 1101(17)(E) and (F)) were repealed in 2021,
    though that does not affect Mulkern's appeal. See 2021 Me. Laws
    ch. 396, § 1.
    - 20 -
    
    854 F.3d 87
    , 95–96 (1st Cir. 2017).6              For that reason, a conviction
    under that Maine law for trafficking heroin or fentanyl does not
    categorically qualify as a "serious drug offense" under ACCA.                 
    Id. at 97
    .          Conversely, in the case of cocaine (and most other
    controlled substances), Maine's statutory regime does require the
    jury to find distributive intent.                 See United States v. Mohamed,
    
    920 F.3d 94
    , 104 (1st Cir. 2019).            Hence, a conviction under Maine
    law for trafficking cocaine categorically qualifies as a serious
    drug offense under ACCA.           
    Id.
    The record is clear that both parties and the court were
    well familiar with the foregoing differential treatment under ACCA
    between         a     conviction   under     Maine      law    for   trafficking
    heroin/fentanyl and, as most relevant here, a conviction for
    trafficking cocaine.            So, if defense counsel thought that the
    government could not prove by proper evidence that the prior
    convictions were for trafficking in cocaine, the apt argument was
    readily apparent:          Such a failure would have required the court to
    assume that the convictions did not involve an intent to distribute
    and thus could not support an ACCA sentence.
    Instead of pursuing the cocaine/heroin dichotomy, the
    defendant's sentencing memorandum started with the premise that
    both       of   his   Maine   trafficking    convictions      "primarily   involve
    6The 2017 Mulkern case is unrelated to this proceeding,
    despite the common surname.
    - 21 -
    cocaine."         He    specifically      identified      as     the    "pertinent
    trafficking statute" the one that "deal[s] with the 14 grams or
    more   of   cocaine."         That    statute    allows   for     a    "permissible
    inference" of intent to distribute based on the quantity of cocaine
    possessed,    Me.      Rev.   Stat.     Ann.    tit. 17-A,       § 1103(3)(B),    a
    mechanism which we held in Mohamed does not equate to taking the
    question of intent away from the jury, contrary to the Maine regime
    for heroin at the time.         See 920 F.3d at 104–05; see also Francis
    v. Franklin, 
    471 U.S. 307
    , 314 (1985) ("A permissive inference
    does not relieve the State of its burden of persuasion because it
    still requires the State to convince the jury that the suggested
    conclusion    should     be    inferred    based    on    the    predicate    facts
    proved.").    Mulkern then argued that his conviction under that
    statute did not qualify as an ACCA offense because, in his view,
    "[a]ll that is required [under that statute], is that the possessor
    possessed the requisite amount of cocaine, and nothing in the
    available documents shows the Defendant in this case pled guilty
    to intending to manufacture or distribute cocaine either."                       In
    short, he first conceded that he was convicted of trafficking
    cocaine, and      he   contended only       that our decision in            Mohamed
    construing that offense as requiring a finding of distributive
    intent was wrong.
    Defense counsel at sentencing continued to argue for
    narrowing    or   rejecting     Mohamed's       holding   that    trafficking    in
    - 22 -
    cocaine    under   Maine   law   was   an   ACCA-qualifying   serious   drug
    offense.    Counsel noted that the district courts in Mohamed and
    Mulkern, even with the benefit of so-called "Shepard proceedings,"7
    ruled against the government.          In the course of that argument,
    counsel stated that the particular Shepard documents filed at that
    point in this case by the government "don't really give us much
    information at all, other than confirming that Mr. Mulkern was
    convicted of a drug trafficking offense under [Maine law]." Alert,
    if not paranoid, government counsel promptly sought clarification.
    [GOVERNMENT COUNSEL]: . . . [B]ased upon the
    -- the sentencing memorandum filed by the
    defendant and the arguments presented in those
    filings, it was the Government's understanding
    that there's no dispute that the prior
    convictions involved cocaine, and so I wanted
    to confirm that that is not a disputed issue
    before I not offer any more exhibits.
    THE COURT: [Defense Counsel], is there any
    dispute on that question?
    [DEFENSE COUNSEL]: No, Your Honor.
    THE COURT: All right. So that is established,
    that they did involve cocaine.
    The government then went on to explain why it sought
    this clarification, emphasizing that "it makes a difference what
    drug we're dealing with" and that "[t]he drug matters," for the
    7  Shepard v. United States, 
    544 U.S. 13
    , 26 (2005), established
    that a court considering an ACCA sentence may consult certain limited
    documents relating to a divisible prior offense to determine whether
    the defendant was convicted of a form of that offense that qualifies
    as an ACCA predicate.
    - 23 -
    reasons outlined above.            In the course of this explanation, the
    government    explicitly       relied      on     its    perfectly     reasonable
    understanding of Mulkern's concession, that the disputed offenses
    "did involve cocaine" and "didn't involve heroin or fentanyl."
    The     court   summarized      the   government's       argument   as
    essentially saying that "because the crime was cocaine, intent had
    to be proven," before inviting defense counsel to respond to that
    summary.    In doing so, defense counsel did not once mention heroin
    or fentanyl, or in any way suggest that either prior conviction
    was   or   could    have    been    for   trafficking    heroin   or    fentanyl.
    Instead, he argued that Mohamed was wrong to hold that cocaine
    trafficking under Maine law qualified as an ACCA serious drug
    offense and urged the court to adopt the dissenting position in
    that case.
    Having heard the foregoing, the district court noted
    that it had to follow Mohamed since "this case involves cocaine,
    a different drug" than the heroin involved in our 2017 Mulkern
    decision.     The court then asked defense counsel "is there any
    aspect of these legal issues I have not addressed that needs to be
    addressed?"       "No," replied defense counsel.
    On appeal, Mulkern now points out that the Shepard
    documents    that    the    government     did    file   in   reliance    on    his
    concessions do not -- at least for one offense -- make clear
    - 24 -
    whether the conviction was for trafficking cocaine or heroin.                    As
    to his apparent waiver of this argument, he advances two theories.
    First, he contends that defense counsel did argue in the
    district court that the Shepard documents (introduced by the
    government) were insufficient to determine under which prong of
    Maine's drug trafficking statute Mulkern was convicted.                         But
    setting aside whether this form of the argument was ever actually
    sufficiently articulated, the mere suggestion that defense counsel
    may have been raising this very argument prompted the government's
    request for clarification as to whether Mulkern was back-tracking
    on his concession in his sentencing memorandum that the "pertinent
    trafficking statute" was the one that "deal[s] with the 14 grams
    or more of cocaine."        If so, the government reserved the right to
    offer   additional    Shepard      documents.     Quite      plainly,    defense
    counsel    then   assured    the   government    and   the    court     that    the
    convictions involved cocaine.        Hence, no additional documents were
    offered.
    Were there any doubt about the scope of the stipulation,
    the   government   and   the    court   made    patently     clear    that     they
    understood the defendant to be conceding that "both of these
    convictions involve cocaine, trafficking cocaine, not trafficking
    - 25 -
    heroin or fentanyl."            That natural reading of the concession,
    understandably, prompted no protest from Mulkern's counsel.
    Picking at bits and pieces of what was said in the
    district      court,    Mulkern    quotes     a    partial    sentence      from   his
    sentencing      memorandum       stating,     "[N]othing       in   the     available
    documents shows the Defendant in this case pled guilty to intending
    to manufacture or distribute cocaine either."                   He contends that
    this shows his argument below was broader than what we have
    described.     But as we noted above, the full quoted sentence reads:
    "All   that    is    required,    is   that       the   possessor   possessed      the
    requisite amount of cocaine, and nothing in the available documents
    shows the Defendant in this case pled guilty to intending to
    manufacture or distribute cocaine either." In other words, counsel
    was arguing that there was no support for a finding of intent to
    distribute the cocaine, not that cocaine was not the object of the
    charge.
    Mulkern    next    argues     that    although    both      convictions
    "involved" cocaine, one also may have in fact involved some heroin.
    Therefore, he reasons, the admission that the case involved cocaine
    did not necessarily mean that the actual charge on which he was
    convicted was for trafficking cocaine.                  This argument, too, fails
    in context.         As we have explained, it is clear from the full
    backdrop of the district court's question to counsel that the court
    was not concerned with the nature of the conduct in fact, but
    - 26 -
    rather the nature of the offense charged. In that context, defense
    counsel at sentencing unequivocally assured the court that Mulkern
    had been convicted of trafficking cocaine, and he then acquiesced
    in repeated characterizations that the convictions did not involve
    heroin or fentanyl.
    Citing United States v. Kennedy, Mulkern next points out
    that "trial testimony" cannot fill a hole in the Shepard documents,
    so his lawyer's admission of the "brute facts" of his prior offense
    should not either.       See 
    881 F.3d 14
    , 23 (1st Cir. 2018).         But
    Kennedy   refers    to   testimony   given   in   connection   with   the
    adjudication of the prior conviction, not a concession later made
    concerning the nature of that prior conviction.
    Considered within the context of the arguments in the
    sentencing memorandum and at the hearing, the only plausible
    conclusion is that Mulkern "explicitly affirm[ed] . . . in the
    district court" that his prior convictions were for trafficking in
    cocaine, the very fact whose finding he now questions.           Orsini,
    907 F.3d at 119.     He has therefore "intentionally relinquishe[d]
    [and] abandon[ed]" this argument, so we need not consider it on
    the merits.   Id.
    To be sure, there are circumstances -- "hen's-teeth
    rare" -- where we may in our discretion excuse a recognized waiver.
    - 27 -
    Id. at 120.     Mulkern suggests in a footnote of his reply brief
    that this is such a case.        We disagree.
    Excusing waiver may be appropriate where "the equities
    heavily preponderate in favor of such a step."                Nat'l Ass'n of
    Soc. Workers v. Harwood, 
    69 F.3d 622
    , 627 (1st Cir. 1995).                 We
    also consider "whether the failure to advance an argument was
    deliberate or inadvertent."       Sindi v. El-Moslimany, 
    896 F.3d 1
    , 28
    (1st Cir. 2018).
    In this instance, Mulkern gives us no reason to think
    that the waiver was the product any misunderstanding or error of
    law.   Mulkern and his counsel very likely knew or could have
    determined whether his prior offenses were not for trafficking
    cocaine.   Nor was the waiver a slip of the tongue -- it was written
    in the sentencing memorandum and then repeated and confirmed in
    response to direct inquiry by the district court.                Indeed, the
    argument that Mulkern made below proceeded from the very premise
    he now contests.
    Notably, Mulkern even now does not assert that his prior
    conviction    was   not   on   account   of   his   cocaine   dealing.    His
    argument, instead, is that there is insufficient documentation to
    prove that fact but for his concession.             So this is not a case in
    which a waiver might have led the court to sentence under ACCA a
    defendant who was not in fact within its scope.               In short, he is
    in fact precisely the person that Congress wanted to receive an
    - 28 -
    ACCA sentence, and his waiver waives no contention that he is not
    that person.    Rather, it waives only the Sixth Amendment hurdle
    that might have allowed him to avoid that classification.
    Our dissenting colleague misapprehends both our holding
    and what happened in the district court.              Neither we nor the
    district court have relied on any stipulation of law.         Nor did the
    district court rely on just the Shepard documents before it.
    Rather, the district court relied on Mulkern's agreement with the
    prosecution concerning a key fact:            that the pertinent prior
    convictions under Maine's drug distribution laws "did involve
    cocaine" and "didn't involve heroin or fentanyl."             The entire
    discussion in the district court was premised precisely on the
    understanding that that fact was pivotal if Mulkern could not
    convince the court that it should reject this circuit's holding in
    Mohamed.
    Nor is there any reason that the district court need
    have sought more Shepard documents given Mulkern's agreement that
    his conviction was for selling cocaine.       F.R. Evid. 801(d)(2); cf.
    United States v. Serrano-Mercado, 
    784 F.3d 838
    , 847 (1st Cir. 2015
    (no   error    for   district   court    to    rely    on   "unchallenged
    characterization" of a purported ACCA predicate); United States v.
    Rios-Hernandez, 
    645 F.3d 456
    , 463 (1st Cir. 2011) (no clear and
    obvious error for district court to rely on defendant's "apparent
    acquiescence to the characterization of the prior convictions").
    - 29 -
    Were that not so, much of criminal practice in our district courts
    would have to be revamped.    Nor was this, as the dissent argues,
    a stipulation of law; it was a stipulation of fact: that he had
    been convicted under Maine law of dealing cocaine.
    Even were we to excuse that waiver, we would still leave
    Mulkern facing the burden of plain error review, which Mulkern
    fails even to address in his main brief on appeal.       See United
    States v. Rodriguez-Monserrate, 
    22 F.4th 35
    , 40 (1st Cir. 2021)
    (holding that an argument "at best entitled to plain error review"
    was waived where the appellant "ma[de] no attempt to satisfy that
    standard" in his opening brief).
    Excusing that waiver as well, the dissent fashions a
    bespoke version of plain error review that        fails to   account
    successfully for our plain error cases.     In those cases, counsel
    did not go so far as to affirmatively tell the judge that something
    is so.   Rather, counsel only remained silent when something was
    said to be so.   Even in that setting, though, we repeatedly placed
    the burden on the appellant to at least represent that the missing
    documents would support the forfeited position raised on appeal.
    See Serrano-Mercado, 784 F.3d at 848; United States v. Davis, 
    676 F.3d 3
    , 10 (1st Cir. 2012); United States v. Turbides-Leonardo,
    
    468 F.3d 34
    , 40 (1st Cir. 2006).        Here, where counsel was not
    merely silent, but actually assured the court that the prior
    conviction involved cocaine, it should follow a fortiori that the
    - 30 -
    defendant must at least do what we required in our other cases,
    assuming that defendant was entitled to plain error review.
    The   dissent   tries    to      explain   its   more   favorable
    treatment of Mulkern by pointing out that in his waiver he did not
    expressly say that there were Shepard documents confirming that
    the prior conviction was for trafficking cocaine.            This strikes us
    as an immaterial distinction given that his more categorical waiver
    -- in context -- subsumed the underlying facts concerning the state
    records.    The prosecution's contention was that his conviction was
    for dealing cocaine.    He challenged that contention only by saying
    that even cocaine convictions did not qualify because Mohamed was
    wrong.     And when asked, he said -- clearly, in context -- that he
    was not challenging that it was a conviction for dealing cocaine.
    So we do not think that we can say that all he did was neglect to
    argue that the Shepard documents put in so far were themselves not
    sufficient.
    The   observation   that      Mulkern      did   challenge   ACCA
    applicability also strikes us as beside the point.             His challenge
    was not that his prior conviction may have been for trafficking
    heroin.    In context he clearly was agreeing that there was no need
    for the government to do more to show that he had been convicted
    of trafficking cocaine.     What he argued, instead, was the entirely
    separate point that Mohamed was wrongly decided.              And that is an
    argument that he would have made even if the record contained a
    - 31 -
    court   document   unequivocally    attesting   to   his   conviction   for
    trafficking cocaine.
    Finally, our dissenting colleague faults the government
    for not arguing each prong of the plain error test.             But this,
    too, overlooks the well-settled assignment of burdens, which do
    not impose on the government the obligation to argue against each
    prong of a test that the defendant did not even mention in his
    opening brief and which would only be available to the defendant
    were we to forgive his waiver.        See United States v. Rodríguez-
    Torres, 
    939 F.3d 16
    , 40 & n.14 (1st Cir. 2019) (reiterating that
    the party asserting plain error carries the burden of establishing
    its elements and that efforts to do so for the first time in a
    reply brief "come[] too late" and are waived).
    III.
    For the foregoing reasons, the decisions of the district
    court are affirmed.
    - Opinion Concurring in Part and Dissenting in Part Follows -
    - 32 -
    BARRON, Chief Judge, concurring in part and dissenting
    in part. The sentence that Thomas Mulkern received under the Armed
    Career Criminal Act ("ACCA") is both mandatory and long.                    It is
    also plainly not supported by the sole evidence that the District
    Court relied on to impose it -- namely, the only official documents
    from Mulkern's state-court criminal proceedings that the District
    Court "received" during the federal sentencing proceedings.                      For
    that reason, it is not a sentence that has been lawfully imposed.
    The   majority      concludes    otherwise       based    on   what   it
    describes as Mulkern's stipulation of fact to the District Court.
    But, as I will explain, the stipulation that the majority has in
    mind was one of law, rather than fact.        Accordingly, I cannot agree
    that any stipulation that Mulkern may be deemed to have made below
    bars us from considering his legal argument for overturning his
    sentence due to a lack of supporting evidence for it.                And, because
    that   legal   argument   is    plainly    correct,     I    would    vacate     his
    sentence, although I agree with the majority that his conviction
    must be affirmed.
    I.
    Mulkern's sentencing challenge on appeal focuses on what
    he contends is the evident inability, as a matter of law, of the
    so-called Shepard documents on which the District Court relied to
    provide the evidentiary basis for the mandatory, 15-year prison
    term that is at issue.      Shepard v. United States, 
    544 U.S. 13
    , 26
    - 33 -
    (2005) ("We hold that enquiry under the ACCA to determine whether
    a plea of guilty to burglary defined by a nongeneric statute
    necessarily admitted elements of the generic offense is limited to
    the terms of the charging document, the terms of a plea agreement
    or transcript of colloquy between judge and defendant in which the
    factual basis for the plea was confirmed by the defendant, or to
    some comparable judicial record of this information.").                     Those
    documents consist of the official records from the state criminal
    proceedings     in   which    Mulkern    was     convicted       of   two    drug
    "trafficking" crimes under Maine law.
    The    government    submitted       the    Shepard    documents      at
    Mulkern's federal sentencing proceedings to establish that he had
    been convicted of three ACCA-qualifying convictions at the time of
    his firearms possession, thereby requiring the imposition of the
    ACCA's   mandatory    fifteen-year      prison       sentence.        
    18 U.S.C. § 924
    (e)(1).     The government contended based on those specific
    documents that Mulkern had been convicted not only of a "violent
    felony" within the meaning of the ACCA, due to a prior Maine-law
    burglary conviction that he had received, but also of two "serious
    drug offense[s]" within the meaning of that same statute, due to
    the two Maine-law drug "trafficking" convictions that he had
    received as well.     
    Id.
    Mulkern does not dispute on appeal that he was convicted
    of a "violent felony" within the meaning of the ACCA based on his
    - 34 -
    burglary conviction.      But, he argues that, as a matter of law, the
    Shepard documents regarding the two drug "trafficking" convictions
    that the government submitted fail to show that he had been
    convicted of two "serious drug offense[s]."               Those documents, he
    contends, show at most that he had been convicted of one "serious
    drug offense," leaving him with only two (rather than the required
    three)_convictions that qualify as predicate convictions under the
    ACCA.
    Mulkern points out that the relevant Shepard documents
    consist solely of his two judgments of conviction for violating
    Maine's drug "trafficking" statute.          See Me. Rev. Stat. Ann. tit.
    17–A, § 1103(1-A)(A).     He then observes that, at the time of those
    convictions,   that   Maine   statute       set   forth     a       divisible   drug
    "trafficking" offense, as that statute set forth two separate drug
    "trafficking" crimes -- one cocaine-based and one heroin-based.
    See United States v. Mohamed, 
    920 F.3d 94
    , 104-105 (1st Cir. 2019).
    Mulkern contends that this feature of the Maine statute
    is significant because we have held that only one of those two
    state-law   "trafficking"     crimes   qualifies       as       a    "serious   drug
    offense"    under   the    ACCA.       
    18 U.S.C. § 924
    (e)(2)(A)(ii).
    Specifically, he rightly notes that we have held that the one for
    "trafficking" cocaine does qualify, see Mohamed, 920 F.3d at 104-
    105, while the one for "trafficking" heroin does not, see United
    States v. Mulkern, 
    854 F.3d 87
    , 96-97 (1st Cir. 2017).
    - 35 -
    Thus, Mulkern contends that the Shepard documents that
    the government submitted -- namely, the two judgments of conviction
    for his Maine drug "trafficking" crimes -- in and of themselves
    can suffice to show, legally, that he had been convicted of two
    "serious drug offense[s]" only if each judgment of conviction
    specifies on its face that it is for the ACCA-qualifying, cocaine-
    based "trafficking" offense. For, only then could those documents,
    by   themselves,    show   that   neither   of   his   drug   "trafficking"
    convictions    is    for    the     non-ACCA-qualifying,       heroin-based
    "trafficking" offense.      Mathis v. United States, 
    579 U.S. 500
    , 519
    (2016) ("Of course, such record materials will not in every case
    speak plainly, and if they do not, a sentencing judge will not be
    able to satisfy '[the] demand for certainty' when determining
    whether a defendant was convicted of a generic offense." (quoting
    Shepard, 
    544 U.S. at 21
    )).        And, Mulkern goes on to argue, one of
    those two judgments of conviction fails to provide the necessary
    indication that it was for the cocaine-based "trafficking" crime.
    Mulkern does acknowledge that the record before us also
    contains a description of the conduct in which he was engaged when
    he committed the Maine "trafficking" offenses for which he was
    convicted.     That description is set forth in the Pre-Sentence
    Report ("PSR") that the U.S. Office of Probation prepared in
    advance   of   Mulkern's    federal    sentencing.       Mulkern   further
    acknowledges that he did not object to that description of his
    - 36 -
    criminal conduct in his federal sentencing proceedings, and he
    does not dispute the accuracy of that description on appeal.
    But, Mulkern points out that the description of his past
    conduct    in    the     PSR    shows   only      that,   as   to     one    of   the   two
    "trafficking" convictions, he was engaged in "[t]rafficking in
    [s]cheduled [d]rugs" and that, per the PSR, the conduct underlying
    that offense involved both cocaine and heroin.                       Thus, he contends
    that, based on that description of his underlying criminal conduct,
    he     could    have     been    charged       under      Maine      law    either      with
    "trafficking" cocaine or "trafficking" heroin.                       Mulkern therefore
    contends that, even when the PSR's undisputed description of his
    criminal       conduct    is    combined     with      the   relevant        judgment    of
    conviction for drug "trafficking" that is in the record, nothing
    shows that that Maine drug "trafficking" conviction is for the
    ACCA-qualifying, cocaine-based "trafficking" offense.
    In consequence, Mulkern contends that, as a matter of
    law, the record fails to establish that he is subject to the
    mandatory fifteen-year sentence that the ACCA requires, because
    there is simply no document in the record that, as a matter of
    law,     could     establish         that    he     had      three     ACCA-qualifying
    convictions -- rather than, at most, two, based on his prior
    burglary       conviction      and   his    conviction       for    one     cocaine-based
    "trafficking" offense -- at the time of his firearms possession.
    Thus, he contends, the record does not permit the ACCA's mandatory,
    - 37 -
    15-year prison sentence to be imposed on him until the government
    augments that record with additional documents from Mulkern's
    state court criminal proceedings that the District Court has not
    yet seen.
    II.
    Of course, as the government asserts, and the majority
    concludes, Mulkern did not make this potentially winning argument
    below.     He argued at his federal sentencing proceedings only that
    he could not be subjected to the ACCA's mandatory, fifteen-year
    prison sentence even if the record sufficed to show that he had
    been convicted twice for the cocaine-based variant of the state-
    law "trafficking" offense.      That was because, he contended in the
    District Court, we were wrong, as a matter of law, to have held in
    Mohamed that such a cocaine-based "trafficking" crime under Maine
    law is itself a "serious drug offense" under the ACCA, 920 F.3d at
    104-105, given the reasons that we gave in an earlier case for
    holding    that   the   heroin-based   variant   of   that   "trafficking"
    offense is not, Mulkern, 854 F.3d at 96-97.
    I happen to agree with Mulkern that Mohamed was wrongly
    decided.     See Mohamed, 920 F.3d at 107 (Barron, J., dissenting).
    But, this panel, like the District Court, has no power to disregard
    a controlling precedent of this Circuit.         Thus, we have no choice
    but to reject the legal argument that Mulkern made below based on
    Mohamed, just as the District Court had no choice but to do so.
    - 38 -
    The key question for us on appeal therefore reduces to
    this: does Mulkern's failure to make a potentially winning argument
    to the District Court about the legal deficiency of the record on
    which the District Court relied in imposing his sentence bar him
    from making that same argument to us on appeal?       The majority
    concludes that it does, given the way that it understands Mulkern
    to have presented his case below.      It emphasizes in this regard
    that Mulkern's counsel agreed when questioned by the District Court
    that -- based on what the Shepard documents that had been given to
    the District Court showed -- the drug "trafficking" convictions at
    issue were for the cocaine-based rather than the heroin-based
    variant of the drug "trafficking" crime.
    That said, it is not always easy to distinguish the
    knowing abandonment of an argument (waiver) from the failure to
    make one (forfeiture).   See United States v. Antonakopoulos, 
    399 F.3d 68
    , 76 n.7 (1st Cir. 2005); United States v. Campbell, 
    26 F.4th 860
    , 871 (11th Cir. 2022) (en banc).       And, I am not as
    confident as the majority that Mulkern's defense counsel was
    knowingly giving up a seemingly strong argument in pressing the
    alternative one that he wrongly thought was even better.
    Nonetheless, the majority recognizes that a waiver may
    be excused in rare cases.   United States v. Orsini, 
    907 F.3d 115
    ,
    120–21 (1st Cir. 2018) (explaining that a defendant's waiver can
    be excused when the "equities heavily preponderate in favor of
    - 39 -
    such a step," and that "[i]n deciding whether an exception is
    warranted,   we   may   consider   factors   'such   as   whether   the
    inadequately preserved arguments are purely legal, are amenable to
    resolution without additional factfinding, are susceptible to
    resolution without causing undue prejudice, are highly convincing,
    are capable of repetition, and implicate matters of significant
    public concern'" (quoting Nat'l Ass'n of Soc. Workers v. Harwood,
    
    69 F.3d 622
    , 627 (1st Cir. 1995) then Sindi v. El-Moslimany, 
    896 F.3d 1
    , 28 (1st Cir. 2018))).      And so, in what follows, I assume
    that the majority is right to conclude that we are dealing with a
    waiver rather than a forfeiture, because I see no reason not to
    excuse the waiver insofar as there was one.
    I must emphasize, though, that my disagreement with the
    majority is about more than the circumstances in which a waiver
    may be excused. It also concerns how to understand what transpired
    below.
    The majority does not appear to be of the view that
    Mulkern waived the legal argument that he now makes to us merely
    because he took the opposite legal position below.        The majority
    instead appears to be of the view that Mulkern waived that legal
    argument by stipulating to the District Court (even if only
    implicitly) that, as a matter of fact, there were Shepard documents
    in existence that, unlike the ones that the government submitted
    in the federal sentencing proceedings, would suffice, as a matter
    - 40 -
    of law, to show that Mulkern was twice convicted of the cocaine-
    based,   rather   than   the   heroin-based,   variant   of   the    drug
    "trafficking" crime under Maine law.
    But, as I will explain, I cannot agree that Mulkern made
    any such factual stipulation.     As a result, I cannot see how the
    representations that he made below preclude him from successfully
    arguing to us that, as a matter of law, at least one of his prior
    drug "trafficking" convictions was not for what the ACCA deems to
    be a "serious drug offense."
    A.
    The majority does not dispute that the waiver of an
    argument about a "purely legal question," as opposed to the waiver
    of a contention about a question of fact, may be excused.           Sindi,
    896 F.3d at 28. And, in my view, Mulkern did waive only an argument
    about a purely legal question.
    The only evidence that the District Court identified as
    providing support for its determination that the ACCA sentencing
    enhancement applied to Mulkern consisted of the Shepard documents
    described above -- namely, Mulkern's two judgments of conviction
    for drug "trafficking" under Maine law.         Indeed, the District
    Court was quite clear during Mulkern's sentencing hearing that it
    was only the Shepard documents that it had "received" that provided
    the evidentiary basis for the determination that Mulkern had the
    requisite number of qualifying convictions under the ACCA.
    - 41 -
    Thus, we need not engage in any fact-finding to determine
    whether there is merit to Mulkern's supposedly waived argument
    regarding the insufficiency of the evidentiary basis for the
    imposition of the ACCA's mandatory 15-year prison sentence.                  We
    need only apply the law to the undisputed facts by examining those
    precise Shepard documents in the record on which the District Court
    relied and determining whether, as a matter of law, they show what
    they must under Mathis.      See Mathis, 579 U.S. at 519.
    B.
    Mulkern's    purely    legal     contention   is     also   "highly
    convincing."      Orsini, 907 F.3d at 120–21.          As I have explained,
    the only Shepard documents that pertained to drug offenses that
    the District Court "received" show no more than that each of
    Mulkern's state-law drug "trafficking" convictions was for an
    offense that was set forth in a statute that set forth two separate
    crimes, only one of which qualifies under the ACCA as a "serious
    drug offense."     Moreover, the unobjected-to PSR does not describe
    the conduct by Mulkern that underlies one of these two convictions
    in   a   manner   that   could   show    what   the   relevant    judgment   of
    conviction itself plainly does not -- that it was for the cocaine-
    based "trafficking" crime rather than for the heroin-based one.
    So, under Mathis, the record plainly is not sufficient,
    as a matter of law, to show that Mulkern did have three prior ACCA-
    qualifying convictions.      Instead, the record at most shows that he
    - 42 -
    had only two such convictions -- the one for a "violent felony"
    based on his conviction for burglary and the other for a "serious
    drug offense," based on a drug "trafficking" conviction under Maine
    law for "trafficking" cocaine.         Indeed, I cannot see what possible
    argument there could be to the contrary, given that there is no
    dispute that a conviction for "trafficking" heroin under Maine law
    is not a "serious drug offense" under the ACCA.
    I do recognize that in other cases we have held that
    defendants could not show plain error in arguing for the first
    time on appeal against the application of federal sentencing
    enhancements based on their contentions that the government had
    failed to submit adequate Shepard documents at their federal
    sentencing proceedings.       See United States v. Serrano-Mercado, 
    784 F.3d 838
     (1st Cir. 2015); United States v. Davis, 
    676 F.3d 3
     (1st
    Cir. 2012); United States v. Turbides-Leonardo, 
    468 F.3d 34
     (1st
    Cir. 2006).      But, those cases are not like this one.
    The defendants in those cases had acquiesced, through
    their silence at their federal sentencing proceedings, to the
    characterization        of   the    offenses    underlying     their    prior
    convictions that had been set forth in the PSRs.          On appeal, those
    defendants did correctly point out that there were no Shepard
    documents   in    the   record     sufficient   to   support   the   relevant
    enhancements to their sentences.              Nonetheless, we interpreted
    their silence at sentencing to indicate that some Shepard documents
    - 43 -
    existed that, although not in the record before the sentencing
    courts, would support the enhancements in question.              We thus
    declined to presume on appeal in those cases that, as matter of
    fact, those extra-record Shepard documents -- if revealed -- would
    show something other than what the defendants seemed to accept
    that those documents would show through their failure to challenge
    the PSR's characterization of the nature of the offenses underlying
    their prior convictions.      After all, there was good reason (based
    on the defendants' silence in the face of the PSR) to think the
    defendants were stipulating, as a matter of fact, that Shepard
    documents that would provide the evidentiary basis for their
    sentence could be produced.      See Serrano-Mercado, 784 F.3d at 848
    (noting that there, like Davis, the defendant had not objected to
    either the PSR's or the sentencing judge's characterization of the
    offense, and as a result, "[t]he District Court thus had no Shepard
    documents before it -- nor any request that it obtain and review
    such documents -- that might cast doubt on either the pre-sentence
    report's   assertion   that   the   enhancement   applied   or   on   the
    defendant's apparent agreement with that assertion").
    Here, however, Mulkern did not at any point suggest in
    the proceedings below -- through a failure to object to the PSR's
    characterization of the statutory offense of conviction -- that
    there was in fact some document from his state court proceedings
    that had not been entered into the record but that when produced
    - 44 -
    would reveal what the documents from those state proceedings that
    were in the record did not.   As we have seen, the PSR did not even
    characterize one of Mulkern's two, prior "trafficking" convictions
    as being for "trafficking" cocaine. The PSR stated in the relevant
    respect only that Mulkern had been convicted of "trafficking" a
    "controlled substance" and that that conviction qualified as an
    ACCA predicate.
    Moreover,   the   PSR    also    did   not   describe   Mulkern's
    conduct in committing one of the state-law drug "trafficking"
    crimes of which he was convicted in a way that would require us to
    conclude that the conviction based on that conduct must have been
    for the cocaine-based variant of the Maine "trafficking" offense.
    As Mulkern convincingly explains, the description of his conduct
    in the PSR refers to his having been in possession of both heroin
    and cocaine.   In other words, he seemingly could have been charged
    based on that conduct with either the cocaine- or heroin-based
    variant of Maine's drug "trafficking" offense. Thus, while Mulkern
    did not dispute that description during the sentencing hearing
    below, his failure was not a stipulation to the factual nature of
    his conduct that would compel the conclusion that he was convicted
    for that conduct of "trafficking" cocaine rather than heroin.
    Notably, my understanding of what transpired below is
    not just my own.   The government does not itself contend (as the
    majority necessarily does in relying on the claimed stipulation)
    - 45 -
    that Mulkern, at any point, suggested through either what he did
    say or what he did not that there were any damning, extra-record
    Shepard documents out there that had not been submitted to the
    District Court.   And, indeed, the District Court also appears to
    have understood Mulkern's position at sentencing to have been
    merely that, because Mohamed was wrongly decided, the specific
    Shepard documents that had been entered into the record as to at
    least one his two drug "trafficking" convictions did not suffice,
    as a matter of law, to establish that he had been convicted of a
    qualifying offense under the ACCA even if the conviction was for
    "trafficking" cocaine.
    Thus, the District Court did not suggest that there was
    any factual stipulation by Mulkern to there being extra-record
    Shepard documents that would supply the evidentiary support for a
    15-year mandatory prison sentence under the ACCA.     The District
    Court concluded only that the     Shepard   documents that it had
    "received" supplied that evidentiary basis, given that Mohamed was
    a controlling precedent.
    So, to the extent that the District Court was misled by
    Mulkern due to the argument that he made below about what the
    Shepard documents in question sufficed to show about the type of
    "trafficking" crime of which he had been convicted, the District
    Court was misled solely about a point of law, not a matter of fact.
    For, in crediting the notion that the Shepard documents that it
    - 46 -
    had "received" in and of themselves sufficed to show that Mulkern
    had been convicted twice of "trafficking" cocaine -- and thus that
    those documents in and of themselves sufficed to show that Mulkern
    was subject to the ACCA's fifteen-year, mandatory minimum prison
    sentence -- the District Court was necessarily making a legal
    rather   than   a   factual    judgment    about   what    those     documents
    demonstrated.
    In other words, I do not take issue with the majority's
    suggestion that a defendant (by implication) may be deemed to have
    stipulated to a fact and thereby to have obviated the need for the
    government to put forth evidence to prove that fact.                 I merely
    conclude that we have no such stipulation of fact here.
    Mulkern    did     stipulate    that    the    specific     Shepard
    documents that the government submitted to the District Court --
    namely, the two judgments of conviction for drug "trafficking" --
    showed that he had two prior convictions for "trafficking" cocaine.
    But, Mulkern did not thereby make the factual stipulation that he
    had been twice convicted of "trafficking" cocaine that the majority
    attributes to him.     Instead, the record shows that, by agreeing
    that the Shepard documents before the court sufficed under Mathis
    to show that he had been twice convicted of "trafficking" cocaine,
    Mulkern was making only a stipulation of law concerning the legal
    sufficiency of those documents to reveal that the underlying
    offense was cocaine-based.       But, as I have explained, in light of
    - 47 -
    Mathis,    that    legal    stipulation        was     plainly    wrong,    given      the
    divisible nature of the statute setting forth that offense and the
    facially inconclusive nature of the judgments of convictions that
    the government entered into the record below.
    I do recognize that the government contends that, even
    if we were to excuse Mulkern's waiver below of any challenge to
    whether the submitted Shepard documents could establish, as a
    matter of law, that he had twice been convicted of "trafficking"
    cocaine,    we    still    would     confront      a    waiver    on     appeal.       The
    government contends in this regard that Mulkern has waived on
    appeal any argument that he can show that the District Court
    plainly    erred    in     relying     on   the      Shepard     documents      that    it
    "received" to conclude that the government had met its burden to
    show that he had been convicted of not just one but two prior
    "serious drug offense[s]" within the meaning of the ACCA.                              See
    Serrano-Mercado, 784 F.3d at 845.                 But, I cannot see how that is
    so.
    Mulkern argued to us in his opening brief that he raised
    the   Mathis-based       argument      below    that     he    advances    on   appeal.
    Understandably, then, he did not in that brief address the plain
    error   standard,    as     he   was    asserting       that     there    had   been    no
    forfeiture at all.          Moreover, after the government contended on
    appeal that Mulkern did not in fact raise the Mathis-based argument
    at his federal sentencing proceedings, he filed a reply brief in
    - 48 -
    which he argued both that there was no waiver of that argument and
    that there was at most only a forfeiture of it.                    He then further
    argued that, insofar as there was a forfeiture, he could meet the
    plain error standard.
    So, when confronted with the contention that there was
    a forfeiture, Mulkern argued to us how he could overcome it.                         He
    did so by asserting that the District Court made a clear or obvious
    error in treating the Shepard documents that it had "received" as
    legally    sufficient      to   show    that     he   been   twice    convicted      of
    "trafficking"      cocaine;     that    such     treatment    prejudiced      him    by
    triggering    the   imposition      of    a    mandatory     and    lengthy   prison
    sentence;    and    that    the   error       would   "seriously     impair[]       the
    fairness,     integrity,        [and]     public      reputation      of   judicial
    proceedings."       United States v. Rivera-Morales, 
    961 F.3d 1
    , 12
    (1st Cir. 2020).
    Moreover, I note that the government does not dispute
    that Mulkern has satisfied the prejudice prong of the plain error
    test.     It contends only that he fails to meet the other prongs of
    that test. But, that contention is unpersuasive, given the perfect
    clarity of the legal error here and the evident injustice of
    permitting a defendant to be subject to a fifteen-year mandatory
    prison sentence due to such a clear legal error.                   I add only that,
    in holding the government to its own apparent view that, if there
    were a clear or obvious error, Mulkern was prejudiced by it, I am
    - 49 -
    hardly innovating.       See United States v. Paulino-Guzman, 
    807 F.3d 447
    , 450 n.5 (1st Cir. 2015) ("'[W]hen the government fails to
    request plain error review,' we may 'review the claim under the
    standard of review that is applied when the issue is properly
    preserved below.'" (citing United States v. Encarnación–Ruiz, 
    787 F.3d 581
    , 586 (1st Cir.2015))).
    For   these    reasons,    I    cannot   agree    that      our   prior
    precedents in this realm preclude Mulkern from showing plain error
    here.   None of them involved, as this one does, a sentencing judge
    expressly identifying the specific documents that served as the
    evidentiary   foundation     for     the   application      of   the    relevant
    sentencing enhancement when those documents patently provide no
    such foundation.     Nor are any of those cases ones in which the
    government failed to dispute the defendant's contention that he
    was prejudiced by being subjected to a sentencing enhancement on
    such a barren record.      Accordingly, those cases fail to show that
    we should not excuse the waiver that the majority contends occurred
    insofar as it means to suggest that the legal argument that Mulkern
    now asks us to consider is less than "highly convincing."
    C.
    I recognize that even when a waived argument concerns a
    purely legal contention that is highly convincing, we must take
    account of any possible prejudice to the non-waiving party of our
    excusing the waiver.       But, in asserting that Mulkern is bound by
    - 50 -
    the mistaken legal position that he took below, the government
    does not suggest that Mulkern gained an edge by keeping additional
    evidence of his conduct hidden from the District Court at his
    federal sentencing.      Nor does the government contend that there
    were other Shepard documents that were once available but that
    have since been lost to time.        The government thus does not contend
    that Mulkern's failure to require the government to show its hand
    in the federal sentencing proceedings prejudiced its ability to
    make   a   strong   showing   that    his     two   drug-related,   Maine-law
    convictions were both for ACCA predicate offenses.
    Rather, the government maintains on appeal that there
    are other Shepard documents from Mulkern's state court proceedings
    that were not entered into the record at his federal sentencing
    proceedings in the District Court, that it has those very documents
    in hand, and that it is prepared to reveal them now if asked.             The
    government even notes that it would have shown them to the District
    Court if Mulkern had not agreed that the documents that it had
    entered into the record sufficed to show that he had been convicted
    twice of "trafficking" cocaine.         How hard would it be, then, for
    the government to make those as-yet-unseen documents part of the
    record at this stage of the litigation, whether on appeal or in
    the District Court on remand, so that a court could then determine
    whether one of Mulkern's drug "trafficking" convictions in fact is
    for "trafficking" heroin?
    - 51 -
    In sum, the government is best positioned to know whether
    it would be prejudiced if we were to excuse the waiver.                          Yet, it
    develops no argument as to how it would be prejudiced if we were
    to accept its own offer to have a court look at the mystery Shepard
    documents that it contends that it holds.                   I thus cannot see any
    basis for concluding that our obligation to ensure that we treat
    the non-waiving party fairly requires that we refuse to consider
    Mulkern's meritorious legal contention under Mathis in deciding
    whether to affirm his federal sentence.
    D.
    I    come,   then,     to   the    final    prong    of   the     test   for
    determining whether to excuse the waiver.                  That prong, like prong
    four of the plan error test, asks us to reflect on the relationship
    between   a       decision    as     to   whether    to   excuse      the   waiver     and
    confidence in the judicial system.                But, here, as well, I see more
    reason to excuse the waiver than not to do so.
    The doctrines of waiver and forfeiture play an important
    role in ensuring an orderly process of appellate adjudication.
    See Orsini, 907 F.3d at 119.               But, they exist to facilitate, not
    thwart, the dispensing of justice.                  See, e.g., United States v.
    Torres-Rosario, 
    658 F.3d 110
    , 116 (1st Cir. 2011) (excusing a
    defendant's waiver of objection to his ACCA sentence enhancement
    because   the      plain     error    standard      was   met   and     there    was   "no
    threat . . . of unfair prejudice to the government").
    - 52 -
    The government has no legitimate interest in advocating
    for the imposition of a sentence pursuant to the ACCA if there are
    no Shepard documents that suffice to support the imposition of
    that sentence.    And, the government has not explained how it would
    be prejudiced if we were to make it do what it has not yet
    done -- show a court evidence that could suffice to establish that
    Mulkern was convicted of two, rather than just one, "serious drug
    offense[s]" within the meaning of the ACCA.       Thus, I do not think
    that it reflects well on our system of criminal justice to affirm
    the   mandatory   fifteen-year-long   prison   sentence   in   this    case
    without first requiring a court to review the only evidence (if
    any there be) that could supply the missing record support for the
    imposition of that sentence.
    We have been careful in our past cases to ensure that
    defendants facing sentencing enhancements based on convictions
    arising out of state criminal statutes that set forth divisible
    offenses are not incentivized to hold back contentions about
    deficiencies in the record to gain strategic advantage.               Thus,
    when such defendants have led a sentencing judge to believe that
    there is extra-record evidence that would cinch the case for
    applying the relevant sentencing enhancement, we have been wary of
    permitting those defendants to reverse course on appeal by crying
    foul that no such evidence had been entered at sentencing.
    - 53 -
    Mulkern did not engage, however, in any such strategy.
    He staked his challenge to the imposition of the ACCA-based
    enhancement below on a mistaken legal contention about certain
    specific Shepard documents that had been submitted to the District
    Court.   He now wishes to press the purely legal, and plainly
    correct, contention that he did not make at that time -- namely,
    the contention that those documents fail as a matter of law to
    show what they must.    As that contention is clearly a winning one,
    I can see little justice in affirming a sentence that, as the
    record presently stands, provides no basis for concluding that it
    is a sentence that lawfully may be imposed on him.
    III.
    For   these   reasons,    I   respectfully   dissent   from   the
    majority's decision to affirm the sentence below, although I join
    fully in the rest of the majority's analysis.
    - 54 -