Given that Obama has little to lose at this point in his presidency, Eric Posner dreams. On what legal authority?
[Obama] could cite his commander-in-chief power under the Constitution and argue that Congress cannot force him to detain enemy combatants he believes should be released. It was on that basis that he recently traded five Guantanamo detainees for Bowe Bergdahl, an American solider captured by the Taliban. There are also various statutory loopholes he could exploit. Indeed, the president could declare the war with al-Qaida over, and in this way remove the legal foundation for the remaining Guantanamo detentions. It is perhaps for this reason that the president has announced that he wants a statute from Congress that authorizes the use of force against ISIS.
Once that statute is in place, he could formally declare the war with al-Qaida, and would be able to drop the fiction that ISIS and al-Qaida are the same entity, which he used to justify relying on the statute that authorizes the use of military force against al-Qaida for hostilities with ISIS.
One major constraint on all these actions is that Obama can sustain them only as long as he remains in office. Since he can’t make law, the next president will not be bound to continue them. However, the practical significance of this constraint is nil. If Obama releases Guantanamo detainees, the next president will not be able to put them back in Guantanamo. He or she could reopen Guantanamo and repopulate it with a new batch of terrorists, but the Guantanamo experiment was a failure, and no future president will repeat it.
I’d argue that this is a legitimate use of the president’s wartime executive authority. Would Obama ever do it? Maybe as a final, irreversible act two years from now – like his power to pardon. But it does not seem to me to be likely given the president’s institutional conservatism and aversion to “any sudden moves.” But then, I have no idea what Obama is really like when his long game is done and he really does not have anything left to lose. It sure would be a high note to go out on – the mother of all meep meeps.