In this photo from Nov. 6, U.S. Marines prepare to build a military site during a sandstorm in western Anbar, Iraq, the newest outpost in the fight against the Islamic State. (Khalid Mohammed/AP)

Last week, in honor of Veterans Day, the Monkey Cage ran several military-themed posts, including a survey of how those in uniform view President Trump, research on how many veterans serve in Congress (and why that matters), and the current standing (and ongoing expansion) of the 2001 Authorization for the Use of Military Force (AUMF).

But there’s more to say about that last entry. For while the Trump administration says it already has all the statutory authority it needs, it may come to prefer an unassailable legal footing for the evolving war on terror. There are several reasons for this. One of them is named — for the moment — John Doe.

Some quick background on the AUMF and why it matters

Congress passed the AUMF shortly after the mass murders of Sept. 11, 2001. It gave the president authority to determine who “planned, authorized, committed, or aided the terrorist attacks,” and to use “all necessary and appropriate force against those nations, organizations, or persons” or those that harbored them.

That clearly applies to al-Qaeda and the Taliban. But since the June 2014 start of Operation Inherent Resolve (OIR) against the forces of the so-called Islamic State (ISIS or ISIL), critics have asked whether it can apply to a group that broke sharply with al-Qaeda after an early affiliation, and that did not exist in 2001. The Obama administration argued that the 2001 AUMF extends to “associated forces” of al-Qaeda and that the Islamic State fits that category. As Defense Department general counsel Stephen Preston argued in a 2015 speech, the group “did not spring fully formed from the head of Zeus a year ago. . . . The name may have changed, but the group we call ISIL today has been an enemy of the United States within the scope of the 2001 AUMF continuously since at least 2004.”

The Trump administration seems to have adopted that reasoning. The AUMF is not the only source of authority it has claimed. Responding to questions about the four American soldiers killed in Niger in early October, Secretary of Defense Jim Mattis told the Senate Foreign Relations Committee they were part of a “train and equip” mission authorized by a different law (Title 10 of the U.S. Code, to be precise.) But it is a crucial one. At that same hearing, Secretary of State Rex Tillerson told senators, “The United States has the legal authority to prosecute campaigns against the Taliban, al-Qaeda, and associated forces, including ISIS. . . . The 2001 AUMF remains a cornerstone for ongoing U.S. military operations and continues to provide legal authority relied upon to defeat this threat.”

So who is John Doe, and what does he have to do with the AUMF?

In September, an American citizen captured in Syria while fighting for ISIS was handed over to the U.S. military. He is now being held in Iraq.

That’s a problem. In 2004, the Supreme Court ruled that the AUMF allowed American citizens to be detained and held as “enemy combatants” outside the civilian court system. But such detainees had to receive some measure of due process, including “a meaningful opportunity to contest the factual basis for that detention before a neutral decisionmaker.” In another series of cases, the justices made clear that prisoners held at the Guantanamo Bay facility in Cuba had access to American civilian courts.

All this raises issues for how the administration can deal with John Doe. The first option is to charge him in a civilian court — but doing so would require assembling admissible evidence that can convict him, which could be difficult. A second is to transfer him to Iraqi custody — but doing so risks violating a law against sending prisoners to countries that practice torture.

Third, he could be designated formally as an enemy combatant and moved to Guantanamo Bay. But there’s a catch. Doing so would open the courtroom door — providing a clear legal avenue for asking the courts directly whether the AUMF covers the war against ISIS. The government might prevail. But it might not. As Lawfare’s Benjamin Wittes has noted, “the litigation risk associated with asserting in federal court that the AUMF authorizes the detention of an ISIS fighter is not trivial.”

For the past two months or so, the government has punted on the question by simply holding John Doe incommunicado. The ACLU has filed a lawsuit on his behalf, though it is not clear whether the organization has standing to bring this challenge. But at some point — surely soon? — the administration will have to make a choice.

John Doe isn’t the only possible challenger to the AUMF’s extended use

Nor is this the only possible entry for court consideration of the AUMF. For instance, Moath al-Alwi, a current Guantanamo detainee, argues that the original conflict in Afghanistan covered by the AUMF ended when President Obama declared the end of U.S. combat operations there. Thus, he can no longer be kept in custody. In February, a district court rejected this claim; it is now before the D.C. Circuit Court of Appeals.

A potentially stronger case is also before that court in the form of a lawsuit brought by Army Capt. Nathan Smith against his commander in chief. Smith, who served in Operation Inherent Resolve, has charged that the AUMF did not authorize that conflict. If that’s true, the War Powers Resolution’s 60-day “clock” for the use of force expired long ago, forcing Smith to choose between his officer’s oath to support the Constitution and the illegal orders issued by the president.

As far back as 1804, the Supreme Court held that a presidential order cannot legalize an act forbidden by Congress. The Smith case, if it proceeds, could force courts to clarify the terms of the War Powers Resolution for the first time. The debate is detailed in a useful podcast with Smith’s counsel, Yale Law professor Bruce Ackerman, and Obama National Security Council legal adviser Chris Fonzone.

Given all this — as well as the potential for extending American force to the next degree of separation from al-Qaeda, against far-flung affiliates of the Islamic State — the administration has suggested that perhaps Congress could craft an updated AUMF.

But the administration has conditions — namely, that the AUMF have no conditions. As Lawfare sums up, Tillerson and Mattis told the Senate that “any new AUMF would need to be free of time constraints, geographical constraints or operational limitations; instead they proposed a conditions-based approach that would end the authorization only once certain targets are met. (These targets were not specified.)”

Will Congress write that almost-blank check? Will the courts force their hand? Stay tuned.