Last week, President Trump issued a new executive order reversing the 2009 executive order that had ordered the closure of detention facility at Guantanamo Bay, Cuba and re-asserting its legality under the 2001 Authorization for the Use of Military Force (AUMF) against those responsible for 9/11. The order comes sixteen years after the United States first began detaining individuals at Guantanamo as part of the War on Terror. In this time span, there have been a host of legal and political efforts to move detainees out of the facility. These attempts have met with significant success: Although the detention facility continues to function, the number of people held has fallen from a peak of more than 700 detainees, to just forty-one today.

Getting the detention facility to zero, however, has proven an elusive goal, and this new order may place it further out of reach. But President Trump’s insistence that the authority to hold the longtime detainees remains valid clashes with a new argument that may be gaining traction in the courts: the detentions, even if they were permissible earlier, are no longer legal because of the passage of time.

While a recent habeas petition in Al-Bihani v. Trump has given the U.S. District Court for the District of Columbia a fresh opportunity to consider this issue, a habeas petition already before the U.S. Court of Appeals for the District of Columbia presents its own chance for that court to grapple with the legality of detention at Guantanamo — and in particular, address not simply the question of when detentions have outlived their underlying legal basis, but who gets to decide: Can the executive branch simply assert that hostilities justifying a prisoner’s detention remain active, or will the courts look at the facts to determine whether the relevant conflict is, indeed, ongoing?

The case in question is Moath Hamza Ahmed Al-Alwi v. Donald J. Trump, filed this past October. Like the habeas petitioners in the recent petition lodged in Al Bihani et al., the U.S. Government has held Al-Alwi at Guantanamo for more than fifteen years. Since 2005, Al-Alwi has been seeking a writ of habeas corpus against the U.S. Government. In filings at the U.S. District Court for the District of Columbia earlier this year, he argued that the U.S. Government’s authority to detain him under the 2001 AUMF has terminated because the conflict in which he was captured is no longer in a phase of “active hostilities.” In making this argument, Al-Alwi relied on the 2004 Supreme Court case Hamdi v. Rumsfeld, in which six justices held that the Executive may detain combatants in the War on Terror so long as “active hostilities” remain ongoing in the relevant conflict. The Supreme Court cited to the Third Geneva Convention of 1949 and observed that “[i]t is a clearly established principle of the law of war that detention may last no longer than active hostilities.”  The court denied al-Alwi’s petition for a writ of habeas corpus and granted the government’s motion to dismiss al-Alwi’s challenge to his continued detention at Guantánamo Bay.   Al-Alwi sought initial en banc review in the U.S. Court of Appeals for the District of Columbia, a request that the court denied, converting the challenge into an appeal.

On behalf of experts on international law and foreign relations law, we, together with lawyers at Debevoise & Plimpton, filed an amicus brief in support of Al-Alwi. The brief argued that the international law of war both enables and constrains the president’s authority to detain under the 2001 AUMF.

The AUMF itself contains no explicit detention authorization. In 2004, the Hamdi plurality held that there is an implied authority to detain enemy combatants under the AUMF, explaining that “we understand Congress’ grant of authority for the use of ‘necessary and appropriate force’ to include the authority to detain for the duration of the relevant conflict, and our understanding is based on long-standing law-of-war principles,” (521).

Those law of war principles cited by the Hadmi plurality, in turn, require a fact-based assessment to determine whether hostilities are ongoing. Our brief cites a wide range of sources supporting this proposition, including commentaries to the Geneva Conventions of 1949, manuals used by militaries around the world, judgments of international tribunals, and prior judgments of the U.S. Supreme Court.

One key issue on appeal is just how the court should determine whether “active hostilities” are in fact ongoing–and whether it should simply accept representations made by the executive. In Al-Alwi, the District Court deferred to statements from the executive branch in concluding that active hostilities were ongoing, and therefore that the President retained the authority to detain Mr. Al-Alwi under the AUMF.

As our brief explains, U.S. courts have repeatedly demonstrated willingness and capacity to engage examine the fact when considering law of war questions. For example, in the Prize Cases, the Supreme Court considered factors such as the extent of territory held by rebel parties in determining that a state of civil war existed. In Ex Parte Milligan, the court distinguished the executive’s power to proclaim martial law during wartime from the question of whether the stated war is “actual and present,” considering facts such as the army’s non-presence in Indiana. And in The Protector, the court considered executive statements only after determining that the facts alone were too muddled to decide when the Civil War began and ended. Even in Ludecke v. Watkins, a World War II case, the court considered facts such as the U.S. Army’s activity on the ground in Europe to determine the status of the war.

More recent cases show the same trend of U.S. courts engaging with the facts to determine compliance with the international law of war. The plurality in Hamdi held that the AUMF authorizes detentions “if the record establishes that United States troops are still involved in active combat in Afghanistan.” Similarly, the District Court in Al Warafi v. Obama espoused the importance of facts, ruling that “the President’s position, while relevant, is not the only evidence that matters.”

Around the world, state military manuals also employ factual assessments to determine if hostilities remain active, consistent with international law. The United Kingdom specifies that “‘[c]essation of active hostilities’ is a question of fact and does not depend on the existence of an armistice agreement.” Germany’s interpretation of the “end of active hostilities” in Article 118 of the Third Geneva Convention, governing the release and repatriation of prisoners of war, similarly notes that “[w]hat really matters is the actual cessation of hostilities . . . .” Canada emphasizes the expiration of detention authority “as soon as the reasons which necessitated internment cease to exist,” and “as soon as the circumstances justifying the arrest, detention or internment have ceased to exist.” Furthermore, international law suggests that even simply the ongoing presence of a non-international armed conflict — itself required for detention authority and as background to “active hostilities” — requires a fact-based assessment.

How the D.C. Circuit Court of Appeals comes down on the issue of “active hostilities” will obviously have significant repercussions for the forty-one detainees still at Guantanamo. But the court’s decision will reach far beyond those forty-one detainees.  The lasting legacy of the court’s ruling will turn on its decision as to who decides that these detainees can still be held: Will the court affirm the District Court’s deference to the executive’s representations of the state of active hostilities, thus permitting indefinite detention as long as the executive is willing to state that hostilities remain?  Or will it assert the role of the judicial branch to examine the claims made by the Executive against the facts presented in court before affirming the need for continued detention?

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