Since his State of the Union address on Tuesday, when Obama reiterated that he will "keep working" to shut down the prison, the administration has sped up the effort significantly. Ten prisoners were transferred this week. Ninety-three prisoners remain, 34 of whom have already been cleared for release. On Thursday, Defense Secretary Ash Carter said he had sent a detailed, written plan to Obama laying out how to move the remaining prisoners to the United States. The White House is to submit that plan to Congress soon.
That strategy directly challenges existing laws that not only prevent Obama from moving Guantanamo prisoners to U.S. soil, but also bar the Pentagon from spending congressionally appropriated funds to do so. Obama, in a series of signing statements, has consistently rejected the validity of those laws, arguing they infringe upon the executive's powers.
Military law experts told us that if the White House defies Congress, lawmakers' options for stopping Obama are limited.
"It would be difficult for anyone to intervene," said Rachel VanLandingham, a professor at Southwestern Law School who served as a judge advocate in the Air Force. "If he really wanted to do it, he could, but it would come at a huge political cost."
That cost could include a long court battle over the constitutional separation of powers. But the federal courts are unlikely to intervene quickly because it's largely a political issue, several experts said, meaning that the Obama administration would be history before a final ruling on the legality of its approach. And at that point, the prison could already be closed.
Congressional leaders, including House Speaker Paul Ryan, have said the president's anticipated action could amount to asking the U.S. military to break the law, but the military is not likely to see it that way.
"Military members are required to follow all lawful orders, but there's a legal presumption that orders are lawful," said VanLandingham. "The military is going to salute smartly."
Congress's record on stopping Obama from releasing prisoners is not strong. Congressional leaders were incensed when in 2014, the president used executive authority to release five Taliban commanders from Guantanamo to trade them for U.S. Army soldier Bowe Bergdahl, who is now set to stand trial for desertion. In December, House Armed Service Committee Republicans issued a report that said Obama violated a statute that required a 30-day notification to Congress on the transfer of any detainees. The Government Accountability Office agreed and added that the Pentagon misused funds for the transfer.
Outgoing Southcom commander Gen. John Kelly said last week that the military was directed to transfer the Taliban five secretly, without alerting reporters who were on the base.
"It was a dicey transfer," he said. "All of us were down there. We were doing the transfer, and we never got caught."
Obama has come close to saying he will shut the prison with or without congressional approval. At his year-end press conference, the president said, "We will wait until Congress has definitively said no to a well-thought-out plan with numbers attached to it before we say anything definitive about my executive authority here."
On Tuesday morning, White House Chief of Staff Denis McDonough told reporters that the president would employ "audacious executive action," for the rest of the year, on several issues that could include Guantanamo Bay. He said the main question Obama will use when considering whether to use executive action is, "Why not?"
Asked about Obama's plans to close the prison, Senate Majority Leader Mitch McConnell said Tuesday, "Hopefully, he will fail." He added: "I'm a supporter of Gitmo. I hope it stays open. I think we should add more terrorists to it."
The White House would get support from many Democrats. The ranking Democrat on the Senate Intelligence Committee, Dianne Feinstein, who was against the Bergdahl trade, told us this week the prison should be closed. "It removes one of the biggest drivers of hostility towards this country," she said.
The wild card in such a scenario is Senate Armed Services Committee Chairman John McCain. McCain has traditionally supported closing the prison, but he is frustrated with what he sees as White House intransigence. This week, he told us he was open to considering the plan but skeptical anything the White House submits can get Republican support.
"It depends on the plan. I would support presenting it my colleagues to see if we could get a majority vote," said McCain. "There's been so much unilateral action that there's a lot of anger about this."
Moving the Guantanamo prisoners to U.S. soil has another advantage for the Obama administration; being inside the U.S. makes it possible for prisoners to be tried in civilian courts. By barring transfers from Guantanamo, Congress had kept many of them in the military commissions system and also given the military and intelligence community greater access to interrogate them.
Senate Intelligence Committee Chairman Richard Burr told us the prisoners should stay where they are to maintain that access: "It's still a viable thing to be able to tap back in to these individuals."
When it comes to Guantanamo, the president's "lame duck" status is a misnomer. Politically, he is now free to act without Congress, saving his successor the problem of Guantanamo. But he may spawn a new problem: a court battle over the constitutional separation of powers.
Eli Lake and Josh Rogin write about politics and foreign affairs for Bloomberg View.