Salim Hamdan v. United States , 696 F.3d 1238 ( 2012 )


Menu:
  •  United States Court of Appeals
    FOR THE DISTRICT OF COLUMBIA CIRCUIT
    Argued May 3, 2012                 Decided October 16, 2012
    No. 11-1257
    SALIM AHMED HAMDAN,
    PETITIONER
    v.
    UNITED STATES OF AMERICA,
    RESPONDENT
    On Petition for Review from the
    United States Court of Military Commission Review
    Joseph M. McMillan argued the cause for petitioner.
    With him on the briefs were Harry H. Schneider Jr., Charles
    C. Sipos, Angela R. Martinez, Abha Khanna, Adam
    Thurschwell, and Jahn C. Olson.
    J. Wells Dixon, Shayana D. Kadidal, and Pardiss
    Kebriaei were on the brief for amicus curiae Center for
    Constitutional Rights in support of petitioner.
    David C. Lachman was on the brief for amicus curiae
    International Legal Scholars Terry D. Gill and Gentian Zyberi
    in support of petitioner.
    2
    John S. Summers and Michael J. Newman were on the
    brief for amicus curiae Professor David W. Glazier in support
    of petitioner.
    Gene C. Schaerr and Kimball R. Anderson were on the
    brief for amicus curiae Constitutional Law Scholars in
    support of petitioner.
    Jonathan Hafetz and David Cole were on the brief for
    amicus curiae Japanese American Citizens League, et al. in
    support of petitioner.
    John F. De Pue, Attorney, U.S. Department of Justice,
    argued the cause for respondent. With him on the brief were
    Lisa O. Monaco, Assistant Attorney General for National
    Security, Jeffrey M. Smith, Attorney, Edward S. White,
    Captain, JAGC, U.S. Navy Appellate Counsel, and Francis A.
    Gilligan, Appellate Counsel, Office of the Prosecutor for
    Military Commissions.
    Before: SENTELLE, Chief Judge, KAVANAUGH, Circuit
    Judge, and GINSBURG, Senior Circuit Judge.
    Opinion for the Court filed by Circuit Judge
    KAVANAUGH, with whom Chief Judge SENTELLE joins except
    as to footnote 6, and with whom Senior Judge GINSBURG
    joins except as to footnotes 3, 6, and 8.
    Concurring Opinion filed by Senior Circuit Judge
    GINSBURG.
    KAVANAUGH, Circuit Judge: The United States is at war
    against al Qaeda, an international terrorist organization. Al
    Qaeda’s stated goals are, among other things, to drive the
    United States from posts in the Middle East, to devastate the
    State of Israel, and to help establish radical Islamic control
    3
    over the Greater Middle East. Al Qaeda uses terror to
    advance its broad objectives. Al Qaeda terrorists do not wear
    uniforms, and they target American civilians and members of
    the U.S. Military, as well as U.S. allies. After al Qaeda’s
    attacks on the United States on September 11, 2001, Congress
    authorized the President to wage war against al Qaeda. That
    war continues.
    In war, when the United States captures or takes custody
    of alien enemy combatants or their substantial supporters, it
    may detain them for the duration of hostilities. Moreover, the
    United States may try unlawful alien enemy combatants
    before military commissions for their war crimes. See Hamdi
    v. Rumsfeld, 
    542 U.S. 507
    , 518-24 (2004); Ex parte Quirin,
    
    317 U.S. 1
    , 26-45 (1942).
    This case raises questions about the scope of the
    Executive’s authority to prosecute war crimes under current
    federal statutes.
    This particular dispute involves the military commission
    conviction of Salim Hamdan, an al Qaeda member who
    worked for Osama bin Laden. In 2001, Hamdan was captured
    in Afghanistan. He was later transferred to the U.S. Naval
    Base at Guantanamo Bay, Cuba.
    Hamdan was not just detained at Guantanamo as an
    enemy combatant. He was also accused of being an unlawful
    enemy combatant and was tried and convicted by a military
    commission for “material support for terrorism,” a war crime
    specified by the Military Commissions Act of 2006. See 10
    U.S.C. § 950t(25); see also 10 U.S.C. § 950v(b)(25) (2006)
    (previous codification of same provision).         Hamdan’s
    conviction was based on actions he took from 1996 to 2001 –
    before enactment of the Military Commissions Act. At the
    time of Hamdan’s conduct, the extant federal statute
    4
    authorized and limited military commissions to try violations
    of the “law of war.” 
    10 U.S.C. § 821
    .
    As punishment for his war crime, Hamdan was sentenced
    by the military commission to 66 months’ imprisonment, with
    credit for some time already served. Hamdan’s sentence
    expired in 2008. Although the United States may have
    continued to detain Hamdan until the end of hostilities
    pursuant to its wartime detention authority, see Hamdi, 
    542 U.S. at 518-22
    , Hamdan was transferred in late 2008 to
    Yemen and then released there. Even after his release,
    Hamdan has continued to appeal his U.S. war crimes
    conviction.
    This appeal presents several issues. First, is the dispute
    moot because Hamdan has already served his sentence and
    been released from U.S. custody? Second, does the Executive
    have authority to prosecute Hamdan for material support for
    terrorism on the sole basis of the 2006 Military Commissions
    Act – which specifically lists material support for terrorism as
    a war crime triable by military commission – even though
    Hamdan’s conduct occurred from 1996 to 2001, before
    enactment of that Act? Third, if not, did the pre-existing
    statute that authorized war-crimes military commissions at the
    time of Hamdan’s conduct – a statute providing that military
    commissions may try violations of the “law of war,” 
    10 U.S.C. § 821
     – proscribe material support for terrorism as a
    war crime?
    We conclude as follows:
    First, despite Hamdan’s release from custody, this case is
    not moot. This is a direct appeal of a conviction. The
    Supreme Court has long held that a defendant’s direct appeal
    of a conviction is not mooted by the defendant’s release from
    custody.
    5
    Second, consistent with Congress’s stated intent and so as
    to avoid a serious Ex Post Facto Clause issue, we interpret the
    Military Commissions Act of 2006 not to authorize
    retroactive prosecution of crimes that were not prohibited as
    war crimes triable by military commission under U.S. law at
    the time the conduct occurred.         Therefore, Hamdan’s
    conviction may be affirmed only if the relevant statute that
    was on the books at the time of his conduct – 
    10 U.S.C. § 821
    – encompassed material support for terrorism.
    Third, when Hamdan committed the relevant conduct
    from 1996 to 2001, Section 821 of Title 10 provided that
    military commissions may try violations of the “law of war.”
    The “law of war” cross-referenced in that statute is the
    international law of war. See Quirin, 
    317 U.S. at 27-30
    , 35-
    36. When Hamdan committed the conduct in question, the
    international law of war proscribed a variety of war crimes,
    including forms of terrorism. At that time, however, the
    international law of war did not proscribe material support for
    terrorism as a war crime. Indeed, the Executive Branch
    acknowledges that the international law of war did not – and
    still does not – identify material support for terrorism as a war
    crime. Therefore, the relevant statute at the time of Hamdan’s
    conduct – 
    10 U.S.C. § 821
     – did not proscribe material
    support for terrorism as a war crime.
    Because we read the Military Commissions Act not to
    retroactively punish new crimes, and because material support
    for terrorism was not a pre-existing war crime under 
    10 U.S.C. § 821
    , Hamdan’s conviction for material support for
    terrorism cannot stand. We reverse the judgment of the Court
    6
    of Military Commission Review and direct that Hamdan’s
    conviction for material support for terrorism be vacated. 1
    I
    In 1996, Salim Hamdan traveled from his native Yemen
    to Pakistan and then to Afghanistan to participate in jihad. In
    Afghanistan, Hamdan attended an al Qaeda training camp. At
    the camp, Hamdan received weapons training, met Osama bin
    Laden, and listened to bin Laden’s lectures.
    Later in 1996, Hamdan became an al Qaeda driver. His
    duties included transporting personnel, supplies, and weapons
    between an al Qaeda guesthouse and al Qaeda’s al Farouq
    training camp in Afghanistan. Eventually, Hamdan became
    Osama bin Laden’s personal driver and bodyguard.
    In August 1996, Osama bin Laden publicly declared war
    on the United States. That declaration came after various al
    Qaeda terrorist attacks, including the 1993 bombing of the
    World Trade Center. In 1998, bin Laden issued a fatwa
    calling for the indiscriminate killing of Americans, including
    American civilians. Hamdan was fully aware of bin Laden’s
    public statements targeting the United States.
    1
    Our judgment would not preclude detention of Hamdan until
    the end of U.S. hostilities against al Qaeda. Nor does our judgment
    preclude any future military commission charges against Hamdan –
    either for conduct prohibited by the “law of war” under 
    10 U.S.C. § 821
     or for any conduct since 2006 that has violated the Military
    Commissions Act. Nor does our judgment preclude appropriate
    criminal charges in civilian court. Moreover, our decision concerns
    only the commission’s legal authority. We do not have occasion to
    question that, as a matter of fact, Hamdan engaged in the conduct
    for which he was convicted.
    7
    In August 1998, al Qaeda operatives bombed U.S.
    Embassies in Kenya and Tanzania, killing 257 people,
    including 12 Americans. Hamdan was generally aware that
    such an attack was planned. Around the time of the attack,
    Hamdan assisted Osama bin Laden in evacuating from
    Kandahar and moving around Afghanistan.
    Later in August 1998, asserting the President’s Article II
    power of self-defense, President Clinton ordered the U.S.
    Military to bomb targets in Afghanistan in an attempt to kill
    bin Laden. Bin Laden narrowly avoided being killed in that
    military action.
    In October 2000, at the direction of bin Laden and senior
    al Qaeda leaders, al Qaeda bombed the U.S.S. Cole off the
    coast of Yemen, killing 17 Americans and injuring many
    others. Around that time, Hamdan returned to Afghanistan
    from Yemen.
    In August 2001, Hamdan drove bin Laden to various
    planning meetings in Afghanistan. Several days before
    September 11, 2001, bin Laden told Hamdan that they had to
    evacuate their compound because of an impending operation.
    Hamdan drove bin Laden to Kabul. They later moved to a
    series of locations around Afghanistan.
    On September 11, 2001, al Qaeda attacked the United
    States, killing thousands of civilians and causing massive
    long-term damage to the American economy and way of life.
    In the days following the attacks of September 11, 2001,
    Congress passed and President George W. Bush signed the
    Authorization for Use of Military Force. That law authorized
    the President
    8
    to use all necessary and appropriate force against those
    nations, organizations, or persons he determines planned,
    authorized, committed, or aided the terrorist attacks that
    occurred on September 11, 2001, or harbored such
    organizations or persons, in order to prevent any future
    acts of international terrorism against the United States
    by such nations, organizations or persons.
    Pub. L. No. 107-40, 
    115 Stat. 224
     (2001).
    Consistent with the 2001 Authorization for Use of
    Military Force, President Bush directed the use of force to kill
    or capture and detain al Qaeda operatives, and where
    appropriate to try unlawful al Qaeda combatants who had
    committed war crimes. On October 7, 2001, as part of the
    overall operation, President Bush ordered U.S. troops into
    Afghanistan to wage war against al Qaeda there, as well as
    against the Taliban government that was in control of
    Afghanistan and had been supporting and harboring al Qaeda.
    On November 13, 2001, the President issued an executive
    order establishing military commissions to try al Qaeda
    members and aiders and abettors who had committed war
    crimes as defined under the “laws of war” or other “applicable
    laws.” Military Order of Nov. 13, 2001, 
    66 Fed. Reg. 57,833
    ;
    57,833-34. The executive order did not purport to rely solely
    on the President’s constitutional authority; rather, it cited two
    separate statutes as congressional authorization for the
    President to employ military commissions: the 2001
    Authorization for Use of Military Force and 
    10 U.S.C. § 821
    ,
    the long-standing statute that authorized military commissions
    to try violations of the “law of war.”
    In November 2001, Hamdan was captured in Afghanistan
    while driving toward Kandahar. The car he was driving
    9
    contained two anti-aircraft missiles. Also in the car was an al
    Qaeda-issued document that authorized the bearer to carry a
    weapon in Afghanistan. Hamdan’s captors turned him over to
    U.S. authorities. He was later transferred to Guantanamo
    Bay, Cuba, and the U.S. Military detained him there as an
    enemy combatant.
    At Guantanamo, Hamdan not only was detained as an
    enemy combatant but also was eventually charged with one
    count of conspiracy and was to be tried before a military
    commission as an unlawful enemy combatant who had
    committed war crimes. 2         Hamdan raised various legal
    objections to the prosecution, and the case ultimately wound
    its way to the Supreme Court. The Supreme Court held that
    the military commission rules then in place contravened
    statutory limits because the rules did not comply in certain
    respects with statutory restrictions contained in 
    10 U.S.C. § 836
    . See Hamdan v. Rumsfeld, 
    548 U.S. 557
    , 613-35
    (2006). The Court split 4-3 on and thus did not decide a
    separate issue: whether conspiracy was a cognizable charge in
    a military commission under the “law of war” for purposes of
    
    10 U.S.C. § 821
    . Compare Hamdan, 
    548 U.S. at 595-612
    (Stevens, J., plurality opinion) (conspiracy is not a law of war
    crime), with 
    id. at 697-706
     (Thomas, J., dissenting)
    (conspiracy is a law of war crime). (Justice Kennedy did not
    address that issue; Chief Justice Roberts did not participate in
    the case.)
    2
    Generally speaking, enemy soldiers or combatants are
    considered unlawful enemy combatants when they, for example,
    join or support an organization waging unlawful war or they
    commit specific “acts which render their belligerency unlawful.”
    Ex parte Quirin, 
    317 U.S. 1
    , 31 (1942). For purposes of the war
    against al Qaeda, this concept is now defined by statute. See 10
    U.S.C. § 948a.
    10
    In the Hamdan case, several Justices specifically invited
    Congress to clarify the scope of the President’s statutory
    authority to use military commissions to try unlawful alien
    enemy combatants for war crimes. See Hamdan, 
    548 U.S. at 636
     (Breyer, J., concurring); 
    id. at 636-37
     (Kennedy, J.,
    concurring).
    In the wake of the Supreme Court’s decision in Hamdan,
    Congress enacted a new military commissions statute. See
    Military Commissions Act of 2006, Pub. L. No. 109-366, 
    120 Stat. 2600
    . Of particular relevance here, Congress expanded
    military commissions beyond prosecuting violations of the
    generic “law of war,” spying, and aiding the enemy, which
    were the crimes listed by statute at the time. See 
    10 U.S.C. §§ 821
    , 904, 906. Of most importance here, Congress
    alleviated some of the uncertainty highlighted in Hamdan
    about the phrase “law of war” in 
    10 U.S.C. § 821
     by listing a
    large number of specific war crimes that could be charged by
    military commission, including conspiracy and material
    support for terrorism. See § 3(a), 120 Stat. at 2630. (In 2009,
    Congress enacted a new Military Commissions Act; that law
    did not make changes relevant to this case. See Pub. L. No.
    111-84, 
    123 Stat. 2574
    .)
    After passage of the 2006 Military Commissions Act,
    Hamdan was charged anew before a U.S. military commission
    on one charge of conspiracy and one charge, containing eight
    specifications, of material support for terrorism.
    At his military commission trial, Hamdan was acquitted
    of conspiracy but convicted of five specifications of material
    support for terrorism. In August 2008, he was sentenced to
    66 months’ confinement and credited for having already
    served most of that time.
    11
    When his sentence ended later in 2008, the war against al
    Qaeda had not ended. Therefore, the United States may have
    continued to detain Hamdan as an enemy combatant. See
    Hamdan, 
    548 U.S. at 635
    ; Hamdi v. Rumsfeld, 
    542 U.S. 507
    ,
    518-24 (2004). But in November 2008, Hamdan was
    transferred by the U.S. Military to Yemen, and he was then
    released on or about January 8, 2009, in Yemen.
    After his release, Hamdan nonetheless continued to
    appeal his U.S. military commission conviction. On appeal to
    the en banc Court of Military Commission Review, Hamdan
    argued (i) that Congress lacked authority under Article I of
    the Constitution to make material support for terrorism a war
    crime triable by military commission; (ii) that in any event,
    the 2006 Military Commissions Act, which listed material
    support for terrorism as a war crime, could not be
    retroactively applied to him because his conduct occurred
    from 1996 to 2001; and (iii) that the statute in effect at the
    time of his alleged conduct – 
    10 U.S.C. § 821
    , which limited
    military commissions to violations of the “law of war” – did
    not authorize prosecution of material support for terrorism as
    a war crime. In 2011, the Court of Military Commission
    Review affirmed the conviction. See United States v.
    Hamdan, 
    801 F. Supp. 2d 1247
     (C.M.C.R. 2011) (en banc).
    By statute, Hamdan has an automatic right of appeal to
    this Court. See 10 U.S.C. § 950g.
    II
    We must first address the issue of mootness – that is,
    whether this appeal is moot because Hamdan has been
    released from U.S. custody. Although the parties agree that
    the appeal is not moot, mootness is a jurisdictional question
    that we must independently consider. See United States v.
    12
    Juvenile Male, 
    131 S. Ct. 2860
    , 2864-65 (2011); Sibron v.
    New York, 
    392 U.S. 40
    , 50 n.8 (1968).
    This case is a direct appeal of a military commission
    conviction. In the criminal context, a direct appeal of a
    criminal conviction is not mooted by a defendant’s release
    from custody. See Sibron, 
    392 U.S. 40
    . The Supreme Court
    has so ruled in part because of the collateral legal
    consequences of a conviction – namely, the possibility that
    the defendant could commit or be tried for a new offense, the
    punishment for which could take account of a past conviction.
    Those collateral consequences are of course present in
    virtually all criminal cases (other than, for example, when the
    defendant has died after the conviction and thus obviously
    cannot commit a new offense).             The same collateral
    consequences are present in military commission conviction
    cases. See, e.g., MANUAL FOR MILITARY COMMISSIONS, Rules
    1001(a)(2), 1001(b)(1)(A) (2012) (in military commission
    sentencing, the prosecution may “introduce evidence of
    military or civilian convictions, foreign or domestic, of the
    accused” as an aggravating factor); 
    18 U.S.C. § 3553
    (a)(1)
    (sentencing courts shall take into account “the history and
    characteristics of the defendant”). 3 Applying the relevant
    Supreme Court precedent, we therefore conclude that a direct
    appeal of a military commission conviction is likewise not
    mooted by the defendant’s release.
    To be sure, that principle generally does not apply to the
    habeas context where a detainee is challenging the basis for
    executive detention. Such a habeas case is sometimes moot
    3
    In his concurring opinion, Judge Ginsburg calls for a change
    to existing Supreme Court mootness doctrine. In doing so, Judge
    Ginsburg suggests that Hamdan is in Yemen and has little chance
    of landing in future trouble in the U.S. legal system. Maybe.
    Maybe not.
    13
    after the detainee’s release. See Spencer v. Kemna, 
    523 U.S. 1
    , 8-14 (1998); Gul v. Obama, 
    652 F.3d 12
    , 17 (D.C. Cir.
    2011). In our recent habeas decision in Gul, where a former
    Guantanamo detainee objected to a military detention
    determination after his release, this Court dismissed the case
    as moot.
    But Hamdan is not just a military detainee; he has been
    convicted of a war crime by military commission. Therefore,
    our recent decision in Gul does not control here. Rather, this
    case is controlled by the principle that a direct appeal of a
    conviction is not mooted by the defendant’s release from
    custody.
    This case is not moot.
    III
    Under a law now codified at 
    10 U.S.C. § 821
    , Congress
    has long authorized the Executive to use military
    commissions to try war crimes committed by the enemy. See
    Ex parte Quirin, 
    317 U.S. 1
     (1942). That statute authorizes
    military commissions to try violations of the “law of war” – a
    term, as we explain below, that has long been understood to
    mean the international law of war. See Hamdan v. Rumsfeld,
    
    548 U.S. 557
    , 603, 610 (2006) (plurality); 
    id. at 641
    (Kennedy, J., concurring); Quirin, 
    317 U.S. at 27-30, 35-36
    .
    Two other longstanding statutes separately authorize military
    commission prosecutions for spying and aiding the enemy.
    See 
    10 U.S.C. §§ 904
    , 906. 4
    4
    The “aiding the enemy” proscription in 
    10 U.S.C. § 904
    ,
    which was first codified in the Articles of War of 1806, see
    WILLIAM WINTHROP, MILITARY LAW AND PRECEDENTS 102-03,
    981 (rev. 2d ed. 1920), generally requires breach of a duty of
    14
    After the Supreme Court’s 2006 decision in Hamdan,
    Congress enacted a new military commissions statute that,
    among other things, clarified the scope of the Executive’s
    authority to try war crimes. See Military Commissions Act of
    2006, Pub. L. No. 109-366, 
    120 Stat. 2600
    . Of particular
    relevance here, Congress expanded military commissions
    beyond trying violations of the generic “law of war,” spying,
    and aiding the enemy. Congress instead also listed a large
    number of specific war crimes that could be tried by military
    commission, including conspiracy and material support for
    terrorism. See 
    id.
     § 3(a), 120 Stat. at 2630 (now codified at
    10 U.S.C. § 950t).
    Hamdan argues that Congress lacked authority under
    Article I of the Constitution – namely, the Define and Punish
    Clause – to define material support for terrorism as a war
    crime subject to trial by a U.S. military commission.5
    Hamdan maintains that Congress’s authority under the Define
    and Punish Clause is limited to proscribing offenses that are
    already illegal under international law. And Hamdan contends
    loyalty as well as aid to the enemy. See Hamdan, 
    548 U.S. at
    600-
    01 n.32 (plurality) (“aiding the enemy may, in circumstances where
    the accused owes allegiance to the party whose enemy he is alleged
    to have aided, be triable by military commission”). The breach of
    loyalty requirement is made explicit in the 2006 Military
    Commissions Act, which re-codified the crime. 10 U.S.C.
    § 950t(26) (“Any person subject to this chapter who, in breach of
    an allegiance or duty to the United States, knowingly and
    intentionally aids an enemy of the United States, or one of the co-
    belligerents of the enemy, shall be punished as a military
    commission under this chapter may direct.”) (emphasis added).
    5
    The Define and Punish Clause provides that Congress has the
    power: “To define and punish Piracies and Felonies committed on
    the high Seas, and Offences against the Law of Nations.” U.S.
    CONST. art. I, § 8, cl. 10.
    15
    that material support for terrorism is not a recognized
    international-law war crime. The Government responds that
    Hamdan’s focus on the Define and Punish Clause alone is
    misplaced. According to the Government, the Declare War
    Clause and other war clauses in Article I, as supplemented by
    the Necessary and Proper Clause, independently authorize
    Congress to establish military commissions to try an enemy’s
    war crimes. And the Government further contends that
    Congress’s broad authority under the Declare War Clause is
    not constrained by the evolving and often difficult to discern
    standards of international law. Therefore, as the Government
    sees it, Congress has authority to make material support for
    terrorism a war crime triable by military commission.
    We do not decide that antecedent question. Even
    assuming arguendo that Congress had authority under its
    various Article I war powers to establish material support for
    terrorism as a war crime in the Military Commissions Act of
    2006, 6 we conclude that the Act did not authorize retroactive
    6
    Judge Kavanaugh alone concurs in this footnote. Because
    the question of Congress’s Article I power to make material support
    for terrorism a war crime has been thoroughly briefed and argued,
    because that question is logically antecedent to the ex post facto
    issue, and because of the importance of deciding wartime cases in a
    way that provides clear guidance, Judge Kavanaugh believes it
    appropriate to address the antecedent question – as the Supreme
    Court itself did in resolving similar antecedent issues in both
    Hamdi and Hamdan. See Hamdi, 
    542 U.S. at 516-24, 533-34
    (resolving several “threshold” questions, including whether enemy
    combatants may be detained for the duration of hostilities, before
    concluding that the procedures used to detain Hamdi were
    insufficient); Hamdan, 
    548 U.S. at 593-94
     (resolving antecedent
    question whether relevant statutes generally authorized military
    commissions, before concluding that the commission in Hamdan’s
    case contravened separate statutory limits).          Here, Judge
    Kavanaugh would conclude that Congress has authority under
    16
    prosecution for conduct that was committed before the Act’s
    enactment and was not prohibited by U.S. law at the time the
    conduct occurred. Here, Hamdan’s conduct occurred from
    1996 to 2001 – before enactment of the Military Commissions
    Act. And as we will explain, the federal statute in effect at
    the time of Hamdan’s conduct – 
    10 U.S.C. § 821
     – did not
    authorize prosecution for material support for terrorism.
    A
    As is clear from the text of the Military Commissions Act
    of 2006, Congress was quite concerned about the ex post
    Article I, § 8 to establish material support for terrorism as a war
    crime that, when committed by an alien, may be tried by military
    commission. Although material support for terrorism is not yet an
    international-law war crime, Congress’s war powers under Article I
    are not defined or constrained by international law. The Declare
    War Clause and the other Article I war powers clauses do not refer
    to international law, unlike the Define and Punish Clause.
    Moreover, Congress has long prohibited war crimes beyond those
    specified by international law. See 
    10 U.S.C. § 904
     (aiding the
    enemy); 
    id.
     § 906 (spying); cf. Quirin, 
    317 U.S. 1
    . The U.S.
    Constitution does not give the international community – either
    directly, or indirectly through the vehicle of international law – a
    judicially enforceable veto over Congress’s exercise of its war
    powers. Put simply, the United States may be a leader in the
    international community, not just a follower, when Congress
    authorizes war against a terrorist organization or makes crimes such
    as material support for terrorism war crimes triable by military
    commission. To be sure, it is often prudent for Congress and the
    President to coordinate closely with the international community
    and pay careful attention to international law when authorizing war
    and enacting war crimes. But those policy factors, political
    realities, and international-law considerations are not constitutional
    constraints incorporated into the Article I war powers clauses and
    thereby enforceable in U.S. courts.
    17
    facto implications of retroactively prosecuting someone under
    the Act for conduct committed before its enactment.
    Congress tried to deal with any ex post facto problem by
    declaring in the text of the statute that “[t]he provisions of this
    subchapter codify offenses that have traditionally been triable
    by military commissions. This chapter does not establish new
    crimes that did not exist before its enactment, but rather
    codifies those crimes for trial by military commission.”
    § 3(a), 120 Stat. at 2624. The Act continued: “Because the
    provisions of this subchapter (including provisions that
    incorporate definitions in other provisions of law) are
    declarative of existing law, they do not preclude trial for
    crimes that occurred before the date of the enactment of this
    chapter.” Id.
    As Congress well understood when it appended this
    unusual statement to the statute, the U.S. Constitution bars
    Congress from enacting punitive ex post facto laws. See U.S.
    CONST. art. I, § 9, cl. 3 (“No Bill of Attainder or ex post facto
    Law shall be passed.”). Among other things, the Ex Post
    Facto Clause bars laws that retroactively punish conduct that
    was not previously prohibited, or that retroactively increase
    punishment for already prohibited conduct. See Collins v.
    Youngblood, 
    497 U.S. 37
    , 42 (1990); Calder v. Bull, 
    3 U.S. 386
     (1798) (opinion of Chase, J.). The Ex Post Facto Clause
    thus prevents Congress and the Executive from retroactively
    applying a federal criminal statute to conduct committed
    before the statute was enacted.
    As Congress itself recognized in the statutory text,
    retroactive prosecution by military commission could
    similarly raise serious constitutional issues, at the very least.
    As stated in the statutory text, however, Congress believed
    that the Act codified no new crimes and thus posed no ex post
    facto problem. As we explain below, Congress’s premise was
    18
    incorrect. The statute does codify some new war crimes,
    including material support for terrorism. The question for ex
    post facto purposes is this: If Congress had known that the
    Act was codifying some new crimes, would Congress have
    wanted the new crimes to be enforced retroactively? To begin
    with, the statutory text reveals a tight causal link between (i)
    Congress’s belief that the statute codified only crimes under
    pre-existing law and (ii) Congress’s statement that the statute
    could therefore apply to conduct before enactment. That
    causal link suggests that Congress would not have wanted
    new crimes to be applied retroactively. The Executive Branch
    agrees with that interpretation of the statute, stating:
    “Congress incorporated ex post facto principles into the terms
    of the MCA itself.” Brief for the United States at 66. At a
    minimum, we know that the statutory text does not
    contemplate or address the possibility of retroactively
    applying new crimes, leaving us with at least something of an
    ambiguity. And courts interpret ambiguous statutes to avoid
    serious questions of unconstitutionality. See Rapanos v.
    United States, 
    547 U.S. 715
    , 738 (2006) (plurality opinion of
    Scalia, J.) (constitutional avoidance where statute “raises
    difficult questions” of constitutionality); Cherokee Nation of
    Oklahoma v. Leavitt, 
    543 U.S. 631
    , 646 (2005) (avoiding an
    interpretation that “may violate the Constitution”). To avoid
    the prospect of an Ex Post Facto Clause violation here, we
    interpret the Military Commissions Act of 2006 so that it does
    not authorize retroactive prosecution for conduct committed
    before enactment of that Act unless the conduct was already
    prohibited under existing U.S. law as a war crime triable by
    military commission. In this case, therefore, Hamdan’s
    conviction stands or falls on whether his conduct was
    prohibited by the pre-existing statute, 
    10 U.S.C. § 821
    , at the
    time he committed the conduct. 7
    7
    To be clear, we do not here decide whether or how the Ex
    19
    B
    Before enactment of the Military Commissions Act in
    2006, U.S. military commissions could prosecute war crimes
    under 
    10 U.S.C. § 821
     for violations of the “law of war.” The
    Government suggests that at the time of Hamdan’s conduct
    from 1996 to 2001, material support for terrorism violated the
    “law of war” referenced in 
    10 U.S.C. § 821
    . It is true that in
    the text of the Military Commissions Act of 2006, Congress
    declared its belief that material support for terrorism was a
    pre-existing crime under the law of war and thus under 
    10 U.S.C. § 821
    . See § 3a, 120 Stat. at 2624. But exercising our
    independent review, as we must when considering the ex post
    facto implications of a new law, see Calder v. Bull, 
    3 U.S. 386
     (1798) (opinion of Chase, J.); Marbury v. Madison, 
    5 U.S. 137
     (1803), we conclude otherwise. Material support for
    terrorism was not a war crime under the law of war referenced
    in 
    10 U.S.C. § 821
     at the time of Hamdan’s conduct.
    Analysis of this issue begins by determining what body
    of law is encompassed by the term “law of war” in 
    10 U.S.C. § 821
    . The Supreme Court’s precedents tell us: The “law of
    war” referenced in 
    10 U.S.C. § 821
     is the international law of
    war. 8 See Hamdan, 
    548 U.S. at 603
     (plurality) (act is law of
    Post Facto Clause might apply to this case. As we interpret the
    statute, that ultimate constitutional question need not be decided.
    8
    It has been suggested that courts should not use international
    law as a free-floating tool to alter how the courts would otherwise
    interpret a domestic U.S. statute when the statute does not
    incorporate or refer to international law. See Al-Bihani v. Obama,
    
    619 F.3d 1
    , 5-8 (D.C. Cir. 2010) (Brown, J., concurring in denial of
    rehearing en banc); 
    id. at 9-23
     (Kavanaugh, J., concurring in denial
    of rehearing en banc). But that interpretive issue is not implicated
    in this case. As Congress has often done, and as explained in an Al-
    Bihani concurrence, Congress here explicitly referred to
    20
    war offense when “universal agreement and practice both in
    this country and internationally” recognize it as such)
    (internal quotation marks omitted); id. at 610 (analyzing
    international sources to determine whether conspiracy was
    “recognized violation of the law of war”); id. at 641
    (Kennedy, J., concurring) (“the law of war” referenced in 
    10 U.S.C. § 821
     “derives from rules and precepts of the law of
    nations” and is “the body of international law governing
    armed conflict”) (internal quotation marks omitted); Quirin,
    
    317 U.S. at 29
     (“law of war” referenced in 
    10 U.S.C. § 821
     is
    a “branch of international law”); 
    id. at 27-28
     (The “law of
    war” is “that part of the law of nations which prescribes, for
    the conduct of war, the status, rights and duties of enemy
    nations as well as of enemy individuals.”); see also
    Instructions for the Government of Armies of the United
    States in the Field (Lieber Code), General Orders No. 100,
    arts. 27 & 40 (Apr. 24, 1863) (describing the law of war as a
    “branch” of the “law of nations”); O.L.C. Memorandum from
    Patrick F. Philbin to Alberto R. Gonzales 5 (Nov. 6, 2001)
    (“laws of war” are “considered a part of the ‘Law of
    Nations’”); 
    id. at 29
     (“the term ‘law of war’ used in 
    10 U.S.C. § 821
     refers to the same body of international law now
    usually referred to as the ‘laws of armed conflict’”). 9
    international law and explicitly incorporated international norms
    into domestic U.S. law in 
    10 U.S.C. § 821
     by means of the express
    cross-reference to the “law of war.” See 
    id. at 10, 13-15
    (Kavanaugh, J., concurring in denial of rehearing en banc)
    (explaining that distinction).
    9
    See also Curtis A. Bradley & Jack L. Goldsmith, The
    Constitutional Validity of Military Commissions, 5 GREEN BAG 2d
    249, 256 (2002) (“As noted above, President Bush’s Military
    Order, 
    10 U.S.C. § 821
    , and Supreme Court precedent all indicate
    that the jurisdiction of military commissions extends (at least) to
    violations of the international laws of war.”); Maj. Michael A.
    21
    We turn, then, to the question whether material support
    for terrorism is an international-law war crime.
    Newton, Continuum Crimes: Military Jurisdiction Over Foreign
    Nationals Who Commit International Crimes, 153 MIL. L. REV. 1,
    21 (1996) (“Therefore, the entire scope of history and American
    jurisprudence compel the conclusion that Article 21 grants
    jurisdiction only over violations of the international laws of war.
    The text of Article 21 leads to the same conclusion.”); Ruth
    Wedgwood, Al Qaeda, Terrorism, and Military Commissions, 96
    AM. J. INT’L L. 328, 334 (2002) (“This statutory language” in 
    10 U.S.C. § 821
     “acknowledges that the jurisdiction of military
    commissions is defined by the norms of the customary law of
    nations, namely, the law of war.”).
    Even outside the context of 
    10 U.S.C. § 821
    , the term “law of
    war” in the U.S. Code and precedent generally refers to the
    international law of war. See Madsen v. Kinsella, 
    343 U.S. 341
    , 354
    (1952) (The “law of war” includes that part of “the law of nations”
    which “defines the powers and duties of belligerent powers.”);
    Prize Cases, 
    67 U.S. 635
    , 667 (1863) (“The laws of war, as
    established among nations, have their foundation in reason, and all
    tend to mitigate the cruelties and misery produced by the scourge of
    war.”); Hearings on H.R. 2498 (UCMJ) Before the H. Comm. on
    Armed Servs., 81st Cong. 959 (1949) (Representative Overton
    Brooks, Chairman, House Subcommittee No. 1 on Armed Services:
    “What is a law of war?” Colonel John P. Dinsmore: “‘Law of war’
    is set out in various treaties like the Geneva convention and
    supplements to that.” Representative Brooks: “International law.”
    Colonel Dinsmore: “Yes, sir.”); U.S. ARMY JAG, LAW OF WAR
    HANDBOOK 20 (Maj. Keith E. Puls ed., 2005) (identifying
    “customary international law” – that is, “the ‘unwritten’ rules that
    bind all members of the community of nations” during war as one
    of the two major sources of the law of war, along with conventional
    international law); MANUAL FOR COURTS-MARTIAL UNITED
    STATES, at I-1 (2012) (“The sources of military jurisdiction include
    the Constitution and international law. International law includes
    the law of war.”).
    22
    It is true that international law establishes at least some
    forms of terrorism, including the intentional targeting of
    civilian populations, as war crimes. See, e.g., Rome Statute of
    the International Criminal Court art. 8(2)(b), July 17, 1998,
    2187 U.N.T.S. 90; Geneva Convention Relative to the
    Protection of Civilian Persons in Time of War (Geneva IV),
    art. 33, Aug. 12, 1949, 6 U.S.T. 3516, 75 U.N.T.S. 287;
    COMMISSION OF RESPONSIBILITIES, CONFERENCE OF PARIS
    1919, VIOLATION OF THE LAWS AND CUSTOMS OF WAR 17
    (Clarendon Press 1919) (the Allied Nations condemned
    Germany for “the execution of a system of terrorism” after
    World War I).
    But the issue here is whether material support for
    terrorism is an international-law war crime. The answer is
    no. International law leaves it to individual nations to
    proscribe material support for terrorism under their domestic
    laws if they so choose. There is no international-law
    proscription of material support for terrorism.
    To begin with, there are no relevant international treaties
    that make material support for terrorism a recognized
    international-law war crime. Neither the Hague Convention
    nor the Geneva Conventions – the sources that are “the major
    treaties on the law of war” – acknowledge material support
    for terrorism as a war crime. See Hamdan, 
    548 U.S. at 604
    (plurality); Geneva Convention Relative to the Protection of
    Civilian Persons in Time of War (Geneva IV), Aug. 12, 1949,
    6 U.S.T. 3516, 75 U.N.T.S. 287; Hague Convention (IV)
    Respecting the Laws and Customs of War on Land and Its
    Annex, Oct. 18, 1907, 
    36 Stat. 2277
    .
    Nor does customary international law otherwise make
    material support for terrorism a war crime. Customary
    international law is a kind of common law; it is the body of
    23
    international legal principles said to reflect the consistent and
    settled practice of nations. See RESTATEMENT (THIRD) OF
    FOREIGN RELATIONS LAW OF THE UNITED STATES § 102(2)
    (1987) (“Customary international law results from a general
    and consistent practice of states followed by them from a
    sense of legal obligation”). It is often difficult to determine
    what constitutes customary international law, who defines
    customary international law, and how firmly established a
    norm has to be to qualify as a customary international law
    norm. Cf. Sosa v. Alvarez-Machain, 
    542 U.S. 692
     (2004). 10
    10
    Although customary international law, including the
    customary international law of war, contains some well-defined
    prohibitions at the core, the contours of customary international law
    are imprecise. That imprecision provides good reason for Congress
    and the Executive, when they want to outlaw violations of
    perceived international-law norms, to enact statutes outlawing
    specific conduct, rather than simply prohibiting violation of
    something as vague as “international law” or “the law of nations”
    or the “law of war.” Congress has done so in many recent statutes,
    including the Military Commissions Act of 2006. Pub. L. No. 109-
    366, 
    120 Stat. 2600
     (2006). See also War Crimes Act of 1996, Pub.
    L. No. 104-192, 
    110 Stat. 2104
    ; Torture Victim Protection Act of
    1991, Pub. L. No. 102-256, 
    106 Stat. 73
     (1992); Foreign Sovereign
    Immunities Act of 1976, Pub. L. No. 94-583, 
    90 Stat. 2891
    .
    At the same time, the imprecision of customary international
    law calls for significant caution by U.S. courts before permitting
    civil or criminal liability premised on violation of such a vague
    prohibition. Cf. Sosa v. Alvarez-Machain, 
    542 U.S. 692
     (2004). A
    general prohibition against violations of “international law” or the
    “law of nations” or the “law of war” may fail in certain cases to
    provide the fair notice that is a foundation of the rule of law in the
    United States. Therefore, as the Supreme Court required in an
    analogous context in Sosa, and as the plurality suggested in
    Hamdan, imposing liability on the basis of a violation of
    “international law” or the “law of nations” or the “law of war”
    24
    But here, the content of customary international law is
    quite evident. Material support for terrorism was not a
    recognized violation of the international law of war as of 2001
    (or even today, for that matter). As we have noted, the
    Geneva Conventions and the Hague Convention do not
    prohibit material support for terrorism. The 1998 Rome
    Statute of the International Criminal Court, which catalogues
    an extensive list of international war crimes, makes no
    mention of material support for terrorism. See Rome Statute
    of the International Criminal Court, July 17, 1998, 2187
    U.N.T.S. 90. Nor does the Statute of the International
    Tribunal for the Former Yugoslavia, the Statute of the
    International Tribunal for Rwanda, or the Statute of the
    Special Court for Sierra Leone. See Statute of the
    International Tribunal for the Former Yugoslavia, adopted by
    S.C. Res. 827, U.N. Doc. S/RES/827 (1993), reprinted in 32
    I.L.M. 1159, 1192; Statute of the International Tribunal for
    Rwanda, adopted by S.C. Res. 955, U.N. Doc. S/RES/955
    (1994), reprinted in 33 I.L.M. 1598, 1602 (includes terrorism
    itself as a crime); Statute of the Special Court for Sierra
    Leone art. 3(d), Jan. 16, 2002, 2178 U.N.T.S. 138 (same).
    Nor have any international tribunals exercising common-law-
    type power determined that material support for terrorism is
    an international-law war crime.
    Commentators on international law have similarly
    explained that material support for terrorism is not an
    international-law war crime. See, e.g., ANDREA BIANCHI &
    YASMIN NAQVI, INTERNATIONAL HUMANITARIAN LAW AND
    TERRORISM 244 (2011) (“there is little evidence” that a
    proscription of “material support for terrorism” is “considered
    generally must be based on norms firmly grounded in international
    law. See Sosa, 
    542 U.S. at 724-38
    ; Hamdan, 
    548 U.S. at
    602-03 &
    n.34, 605 (plurality). In this case, the asserted norm has no
    grounding in international law, much less firm grounding.
    25
    to be part of the laws and customs of war”). Nor is the
    offense of material support for terrorism listed in the JAG
    handbook on the law of war. See U.S. ARMY JAG, LAW OF
    WAR HANDBOOK (Maj. Keith E. Puls ed., 2005); see also
    Jennifer K. Elsea, The Military Commissions Act of 2006:
    Analysis of Procedural Rules and Comparison with Previous
    DOD Rules and the Uniform Code of Military Justice 12
    (CRS, updated Sept. 27, 2007) (“defining as a war crime the
    ‘material support for terrorism’ does not appear to be
    supported by historical precedent”) (footnote omitted).
    In short, neither the major conventions on the law of war
    nor prominent modern international tribunals nor leading
    international-law experts have identified material support for
    terrorism as a war crime. Perhaps most telling, before this
    case, no person has ever been tried by an international-law
    war crimes tribunal for material support for terrorism.
    Not surprisingly, therefore, even the U.S. Government
    concedes in this case that material support for terrorism is not
    a recognized international-law war crime. No treaty that the
    Government has cited or that we are aware of identifies
    material support for terrorism as a war crime. And the
    Government further admits: The “offense of providing
    material support to terrorism, like spying and aiding the
    enemy, has not attained international recognition at this time
    as a violation of customary international law.” Brief for the
    United States at 48; see also id. at 55-56 (same).
    To be sure, there is a strong argument that aiding and
    abetting a recognized international-law war crime such as
    terrorism is itself an international-law war crime. And there
    are other similar war crimes. But Hamdan was not charged
    with aiding and abetting terrorism or some other similar war
    crime. He was charged with material support for terrorism.
    26
    And as the Government acknowledges, aiding and abetting
    terrorism prohibits different conduct, imposes different mens
    rea requirements, and entails different causation standards
    than material support for terrorism. If the Government
    wanted to charge Hamdan with aiding and abetting terrorism
    or some other war crime that was sufficiently rooted in the
    international law of war (and thus covered by 
    10 U.S.C. § 821
    ) at the time of Hamdan’s conduct, it should have done
    so.
    The Government latches on to a few isolated precedents
    from the Civil War era to prop up its assertion that material
    support for terrorism was a pre-existing war crime as of 2001
    for purposes of 
    10 U.S.C. § 821
    .            There are several
    independent reasons that those cases fail to support the
    Government’s argument. First, the Civil War cases did not
    involve any charges of material support for terrorism.
    Instead, several cases involve guerillas who were punished for
    taking up “arms” as “insurgents” – that is, for direct attacks
    rather than material support. See, e.g., G.O. No. 15, HQ,
    Dep’t of the Mississippi (Apr. 3, 1862), 1 OR ser. II, at 472-
    76. Others were convicted of “joining, aiding and assisting a
    band of robbers and bandits” – in other words, what we would
    likely call aiding and abetting, not material support. G.O. No.
    19, HQ, Dep’t of the Mississippi (Apr. 24, 1862), 1 OR ser.
    II, at 478. In short, those precedents are at best murky
    guidance here. Cf. Hamdan, 
    548 U.S. at 602
     (plurality)
    (requiring “plain and unambiguous” precedent). Second,
    those Civil War commissions were in part military tribunals
    governing certain territory – which are a separate form of
    military commission subject to a separate branch of law, and
    not the kind of law-of-war military commission at issue here.
    As others have suggested, their precedential value is therefore
    limited. See Hamdan, 
    548 U.S. at
    596 n.27; 
    id. at 608
    (plurality) (The “military commissions convened during the
    27
    Civil War functioned at once as martial law or military
    government tribunals and as law-of-war commissions.
    Accordingly, they regularly tried war crimes and ordinary
    crimes together.”) (citation omitted). Third, and perhaps most
    to the point, those cases do not establish that material support
    for terrorism was a war crime recognized under international
    law as of 1996 to 2001 when Hamdan committed his conduct,
    which is the relevant inquiry under 
    10 U.S.C. § 821
    . The
    Government contends that those Civil War precedents
    illuminate what it calls the “U.S. common law of war” – not
    the international law of war. But the statutory constraint here
    imposed by 
    10 U.S.C. § 821
     is the international law of war.
    As the Government told the Supreme Court in Quirin, “This
    ‘common law of war’ is a centuries-old body of largely
    unwritten rules and principles of international law which
    governs the behavior of both soldiers and civilians during
    time of war.” Brief for the United States at 29, in Quirin, 
    317 U.S. 1
     (emphasis added) (citation omitted). To be sure, U.S.
    precedents may inform the content of international law. But
    those Civil War precedents fail to establish material support
    for terrorism as a war crime under the international law of war
    as of 1996 to 2001. And even the Government admits that
    material support for terrorism was not an international-law
    war crime as of 1996 to 2001.
    In short, material support for terrorism was not an
    international-law war crime under 
    10 U.S.C. § 821
     at the time
    Hamdan engaged in the relevant conduct.
    ***
    Because we read the Military Commissions Act not to
    sanction retroactive punishment for new crimes, and because
    material support for terrorism was not a pre-existing war
    crime under 
    10 U.S.C. § 821
    , Hamdan’s conviction for
    28
    material support for terrorism cannot stand. We reverse the
    decision of the Court of Military Commission Review and
    direct that Hamdan’s conviction for material support for
    terrorism be vacated.
    So ordered.
    GINSBURG, Senior Circuit Judge, concurring:       I join
    the decision of the Court but, with respect to its holding Mr.
    Hamdan’s appeal of his criminal conviction by military
    commission is not moot, I do so only because precedent so
    dictates. I write separately to explain the unfortunate state of
    that precedent, which requires us to review the conviction of a
    man long since transferred to Yemen who, even if his
    conviction were overturned and he were to hear of it, would
    not be affected in any way by the result. Because today’s
    decision has no actual consequence for Mr. Hamdan, his case
    is moot in fact, though, curiously, not in law.
    The Supreme Court “presumes” the appeal of a criminal
    conviction is not moot unless “it is shown that there is no
    possibility that any collateral legal consequences will be
    imposed on the basis of the challenged conviction.” Sibron v.
    New York, 
    392 U.S. 40
    , 57 (1968); see United States v.
    Juvenile Male, 
    131 S. Ct. 2860
    , 2864 (2011) (per curiam)
    (“When the defendant challenges his underlying conviction,
    this Court’s cases have long presumed the existence of
    collateral consequences”). The Government concedes, as
    Hamdan’s counsel contends, that it cannot show there is “no
    possibility” Hamdan’s conviction will have a collateral legal
    consequence for him. The parties’ mutual desire to have the
    court decide this case on its merits is of no moment, however;
    an Article III court has an “independent obligation to be sure
    [it] ha[s] jurisdiction,” High Plains Wireless, LP v. FCC, 
    276 F.3d 599
    , 605 (D.C. Cir. 2002), which here requires us to
    determine whether the case has become moot on appeal.
    A criminal conviction may and often does have
    consequences beyond the penalties imposed in the sentence.
    In Sibron, the Court held the defendant’s appeal of his
    conviction was not moot, even though his sentence had
    expired during the pendency of the appeal, because that
    conviction, left undisturbed, could increase his sentence if he
    were later to be convicted of another crime. 
    392 U.S. at 56
    ;
    2
    accord United States v. Morgan, 
    346 U.S. 502
    , 512-13 (1954)
    (“Although the term has been served, the results of the
    conviction may persist. Subsequent convictions may carry
    heavier penalties”). Similarly, in Carafas v. LaVallee, 
    391 U.S. 234
     (1968), the Court concluded that a continuing civil
    disability stemming from a criminal conviction, such as a bar
    to voting in state elections or to serving as a juror, also keeps
    a criminal appeal from becoming moot. Even an adverse
    immigration consequence, including a bar on re-entering
    United States, may suffice to keep a case alive and hence to
    preserve appellate jurisdiction. See, e.g., United States v.
    Hamdi, 
    432 F.3d 115
    , 121 (2d Cir. 2005).
    Although, in considering a challenge to a criminal
    conviction, * “the Court [has] abandoned all inquiry into the
    *
    Contrary to the Court’s reading of the relevant precedents,
    Ct. Op. at 12, the Supreme Court does not distinguish between
    direct review of a criminal conviction and a collateral attack on a
    criminal conviction, by way of a petition for a writ of habeas corpus
    or otherwise. The Supreme Court has, on several occasions,
    indicated the Sibron presumption applies in a collateral proceeding
    for post-conviction relief. See, e.g., Carafas v. LaVallee, 
    391 U.S. 234
     (1968) (holding habeas challenge to criminal conviction not
    moot due to “collateral consequences” of conviction); Lane v.
    Williams, 
    455 U.S. 624
    , 634 (1982) (Marshall, J., dissenting) (“The
    majority recognizes that in habeas corpus challenges to criminal
    convictions, the case ‘is moot only if it is shown there is no
    possibility that any collateral legal consequences will be imposed
    on the basis of the challenged conviction’” (quoting Sibron)).
    Spencer v. Kemna, 
    523 U.S. 1
     (1998), and Gul v. Obama, 
    652 F.3d 12
    , 19 (D.C. Cir. 2011), were habeas cases that did not apply the
    Sibron presumption, but the inapplicability of the presumption did
    not depend upon a distinction between direct review and habeas. In
    Spencer, the petitioner challenged not a criminal conviction but
    rather the revocation of his parole. In Gul, the petitioner challenged
    not a criminal conviction but rather his designation as an enemy
    3
    actual existence of specific collateral consequences and in
    effect presumed that they exist[],” Sibron, 
    392 U.S. at 55
    , the
    presumption is rebutted if the alleged collateral consequences
    are foreclosed as a matter of law. In Perez v. Greiner, 
    296 F.3d 123
     (2d Cir. 2002), the Second Circuit held moot the
    direct appeal of a criminal conviction on the ground there was
    “no material possibility that [the defendant] will suffer
    collateral consequences on the basis of the challenged
    conviction,” 
    id. at 125
    . The defendant in that case had been
    deported when his appeal was heard and was ineligible to re-
    enter the country because of an earlier conviction. With the
    defendant “permanently barred from this country on a wholly
    separate ground, the currently challenged ... conviction
    [could] have no meaningful effect on his admissibility and
    hence [could not] serve as a possible collateral consequence.”
    
    Id. at 126
    .
    Hamdan and the Government each point to a collateral
    consequence of Hamdan’s conviction. Hamdan claims his
    conviction for material support of terrorism makes him
    subject to permanent mandatory exclusion from the United
    States. See 
    8 U.S.C. § 1182
    (a)(3)(B)(i)(I), (V). For its part,
    the Government claims Hamdan’s conviction may expose him
    to an enhanced sentence if in the future he commits a new
    offense and is tried therefore in a civilian or military court of
    the United States. See DEP’T OF DEFENSE, MANUAL FOR
    MILITARY COMMISSIONS, Rule 1001(b)(1)(A) (2010) (“The
    trial counsel may introduce [in a sentencing proceeding]
    evidence of [prior] military or civilian convictions, foreign or
    combatant. Neither decision rested merely upon the ground the
    case sounded in habeas. The present Court’s different view of the
    matter is of no moment, however; as explained below, binding
    precedent unfortunately but unambiguously dictates the Sibron
    presumption applies to the direct review of a criminal conviction,
    such as Hamdan presents here.
    4
    domestic, of the accused”); 
    18 U.S.C. § 3553
    (a)(1)
    (sentencing court shall consider “the history and
    characteristics of the defendant”). The adverse collateral
    consequence raised by Hamdan is foreclosed as a matter of
    law. The adverse collateral consequence posed by the
    Government is so far-fetched that the application of the
    Sibron presumption in this case risks making our opinion
    merely advisory.
    The adverse immigration consequence alleged by
    Hamdan is impossible as a matter of law because Hamdan is
    already subject to mandatory exclusion from the United States
    regardless whether his conviction stands. The Immigration
    and Naturalization Act (INA) provides: “Any alien who ... has
    engaged in a terrorist activity ... is inadmissible.” 
    8 U.S.C. § 1182
    (a)(3)(B)(i)(I). The Government provided overwhelming
    evidence, none of which Hamdan bothers to dispute,
    demonstrating that he engaged in “terrorist activity” within
    the meaning of the INA, including the provision of material
    support for terrorism. * The INA makes Hamdan inadmissible
    *
    The INA defines “[e]ngage in terrorist activity” to include
    committing “an act that the actor knows, or reasonably should
    know, affords material support ...:
    (aa) for the commission of a terrorist activity;
    (bb) to any individual who the actor knows, or reasonably
    should know, has committed or plans to commit a
    terrorist activity; [or]
    (cc) to a terrorist organization ... [designated as such by the
    Secretary of State] ....”
    
    Id.
     § 1182(a)(3)(B)(iv)(VI). A military commission, the Convening
    Authority, and the Court of Military Commission Review each
    separately found beyond a reasonable doubt that Hamdan provided
    material support generally to al Qaeda, and specifically for an act of
    5
    not for his conviction, which we reverse, * but rather for
    having knowingly supported terrorist activities, a historical
    fact we cannot reverse. Cf. Fletcher v. Peck, 10 U.S. (6
    Cranch) 87, 135 (1810) (“The past cannot be recalled by the
    most absolute power”). Nor is it conceivable that an
    immigration court, which applies a standard of proof much
    more favorable to the Government than does a military
    commission, compare 8 U.S.C. § 1229a(c)(2) (“In the
    proceeding [for deciding whether an alien is admissible,] the
    alien has the burden of establishing ... the alien is clearly and
    beyond doubt entitled to be admitted”), with 10 U.S.C. §
    949l(4) (in a military commission “the burden of proof to
    establish the guilt of the accused beyond a reasonable doubt is
    upon the United States”), would find Hamdan in fact had not
    provided any of the five types of material support for which
    he was convicted and therefore may be admitted to the United
    terrorism by, among other things, serving as Osama bin Laden’s
    driver and bodyguard from 1996 to 2001, with the knowledge
    Hamdan “was protecting the leader of al Qaeda” and was
    “facilitating communication and planning used for acts of
    terrorism,” United States v. Hamdan, 
    801 F. Supp. 2d 1247
    , 1259
    (C.M.C.R. 2011); see also 
    id. at 1254, 1258, 1323
    . Al Qaeda has
    been designated as a “foreign terrorist organization” by the State
    Department since 1999. See Designation of Foreign Terrorist
    Organizations, 
    64 Fed. Reg. 55,012
    , 55,012 (Oct. 8, 1999) (initial
    designation); 
    66 Fed. Reg. 51,088
    , 51,089 (Oct. 5, 2001)
    (redesignation).
    *
    Although we reverse Hamdan’s criminal conviction for
    material support, we do so not for lack of evidence but rather
    because the Military Commissions Act of 2006 does not authorize
    retroactive prosecution for an act that was not criminal when done.
    There is no comparable bar to retroactivity that prevents the
    Government from attaching to those same acts adverse immigration
    consequences. See Marcello v. Bonds, 
    349 U.S. 302
    , 314 (1955)
    (“the prohibition of the ex post facto clause does not apply to
    deportation”).
    6
    States. * Because Hamdan is already barred from entering the
    United States due to his past involvement in terrorism, his
    current conviction has no incremental effect upon his
    admissibility and hence the immigration consequence he
    proffers cannot serve as a basis for our jurisdiction. Cf. Gul,
    
    652 F.3d at
    19—20 (where detention at Guantanamo Bay,
    rather than designation as enemy combatant, is the ground for
    inadmissibility, immigration consequence of challenge to
    designation “too speculative to sustain the exercise of our
    jurisdiction”).
    The only other collateral consequence alleged is the
    Government’s preposterously hypothetical prospect of an
    enhanced sentence if Hamdan is in the future convicted in the
    United States for committing another crime. The Supreme
    Court held in Sibron that the hypothetical future sentencing
    enhancement is sufficient to support the presumption that the
    conviction being appealed will have an adverse collateral
    consequence and hence to keep the appeal from being moot.
    Sibron, 
    392 U.S. at 56
    . Subsequent cases, however, cast
    doubt upon the continuing validity of Sibron as applied to this
    case. In Spencer v. Kemna the Court declined to extend the
    Sibron presumption to the appeal of a parole revocation
    *
    In addition to that statutory basis for Hamdan’s permanent
    exclusion, Hamdan would not be physically able to re-enter the
    country because of his automatic inclusion, as a former
    Guantanamo detainee, on the ‘No Fly List.’ See 
    49 U.S.C. § 44903
    (j)(2)(C)(v); cf. Gul v. Obama, 
    652 F.3d 12
    , 19 (D.C. Cir.
    2011) (former detainees are “barred from flights entering the
    United States regardless whether a court declares they were
    unlawfully detained. An order granting a detainee’s habeas petition
    would not mean his exoneration, nor would it be a determination he
    does not pose a threat to American interests; it would mean only
    that the Government has not proven the detainee more likely than
    not ‘materially support[ed]’” terrorism).
    7
    because any collateral consequence in a future sentencing
    “was contingent upon [the defendant again] violating the law,
    getting caught, and being convicted.” 
    523 U.S. 1
    , 15 (1997);
    see also Lane v. Williams, 
    455 U.S. 624
    , 633 n.13 (1982)
    (“The parole violations that remain a part of respondents’
    records cannot affect a subsequent parole determination
    unless respondents again violate state law, are returned to
    prison, and become eligible for parole. Respondents
    themselves are able – and indeed required by law – to prevent
    such a possibility from occurring”).
    That is, although in Sibron a conviction was presumed to
    have adverse consequences for the defendant in a future
    hypothetical sentencing, in Spencer the hypothetical
    sentencing consequences of a defendant’s parole revocation
    were held insufficient to keep his case from being moot
    because such consequences are speculative and depend upon
    future unlawful conduct by the defendant. Both holdings
    were categorical; they did not depend at all upon the
    particular defendant’s probability of recidivating. Therefore,
    the defendants’ future crimes, apprehension, and conviction
    were equally speculative in both cases. It is entirely unclear,
    therefore, how the hypothetical sentencing consequences of a
    parole revocation could be too speculative to support a
    finding of collateral consequences, while the hypothetical
    sentencing consequences of a conviction could be concrete
    and certain enough to support the presumption of collateral
    consequences, and hence Article III jurisdiction, in all
    criminal appeals.
    Nonetheless, “[i]f a precedent of [the Supreme] Court has
    direct application in a case, yet appears to rest on reasons
    rejected in some other line of decisions, the Court of Appeals
    should follow the case which directly controls, leaving to [the
    Supreme] Court the prerogative of overruling its own
    8
    decisions.” Rodriguez de Quijas v. Shearson/Am. Express,
    Inc., 
    490 U.S. 477
    , 484 (1989). Accordingly, because
    Hamdan’s case is a direct appeal of his criminal conviction
    rather than review of a parole revocation as in Spencer, the
    Court is bound to hold the Sibron presumption applies and
    therefore the hypothetical future sentencing consequences of
    Hamdan’s conviction are sufficient to keep his appeal from
    being moot.
    Finally, I note that although this is an “appeal of a
    criminal conviction,” we have strayed far from the familiar
    territory of Sibron and its progeny, which deemed sentencing
    consequences the antidote to mootness.          The criminal
    conviction in each of those cases was entered in a regularly
    constituted civilian court, and the criminal defendant served
    time in a domestic prison before being released into the
    sovereign territory of the United States. As such, upon his
    release the defendant was subject to the criminal laws of the
    United States and of the State in which he was located.
    Recidivism being common in the United States, it is
    unfortunately reasonable to suppose such a defendant may
    again be convicted for violating a state or federal law. * By
    *
    Recidivism rates of convicts released from prisons in the
    United States are well-known and substantial. See DEP’T OF
    JUSTICE, BUREAU OF JUSTICE STATISTICS, RECIDIVISM OF
    PRISONERS RELEASED IN 1994 1 (June 2002) (using a sample of
    272,111 former prisoners in 15 states, study showed 46.9% were
    convicted of another offense within three years of release).
    Recidivism rates among Guantanamo detainees are comparatively
    speculative, but insofar as they are known, are rather modest. See
    DIRECTOR OF NATIONAL INTELLIGENCE, SUMMARY OF THE
    REENGAGEMENT OF DETAINEES FORMERLY HELD AT
    GUANTANAMO BAY, CUBA 1 (March 1, 2012) (of 599 detainees
    released from Guantanamo, 4.7% detained again and “confirmed of
    reengaging” in hostilities over a nine-year period). Presuming that
    9
    contrast, Hamdan is presumably in Yemen and is certainly not
    in the United States; so far as the record shows, he has never
    entered the United States nor expressed any desire to do so;
    and he is barred, both legally and physically, from entering
    the United States. As a result, the only possible future
    sentencing consequence of his conviction by a military
    commission would be through extraterritorial application of
    our criminal law to a federal crime yet to be committed, or
    through a successive prosecution in a military commission for
    a future violation of the law of war. It is, to say the least, far
    more speculative that Hamdan may find himself again being
    sentenced in the United States than it is an domestic criminal
    may recidivate and find himself before a domestic criminal
    court.
    collateral consequences arise from a conviction by a military
    commission for violating the law of war and persist after the
    convict is released into a foreign country, therefore, hardly seems
    justified. Cf. Gul, 
    652 F.3d at 17
     (“not[ing] detention at
    Guantanamo and designation as an enemy combatant are recent
    phenomena; [therefore a court] ha[s] no basis for inferring they
    routinely have collateral consequences”).