The White House will submit the plan to Congress Tuesday outlining the administration's strategy for closing the detention facility for enemy combatants. Disclosure of the plan, mandated by Congress, is bound to meet stiff resistance from Republicans.
The broad outlines of the plan have been known for months, and the White House has said the final product will not contain many surprises in terms of the closure strategy.
The blueprint involves transferring the bulk of remaining detainees to other countries and moving the rest -- who can't be transferred abroad because they're deemed too dangerous -- to an as-yet-undetermined detention facility in the United States.
Obama says the prison -- which holds suspected members of terrorist groups captured overseas -- is a recruiting tool for terrorists and is too costly to maintain.
The number of detainees has dropped to 91 during Obama's time at the White House. There are approximately 2,000 military and civilian personnel assigned to the prison and the facility costs hundreds of millions of dollars to maintain.
A U.S. official told CNN that the report will include broad cost options, however, rather than the detailed specifics requested by Congress.
But lawmakers from both parties have balked at moving Guantanamo detainees into the U.S., making congressional action on the White House plan unlikely.
With Congress expected to dig in its heels, the Obama administration has remained open to taking unilateral action to move prisoners into the U.S.
However, the U.S. military told Congress in January that it is legally prevented from assisting the transfer of detainees to U.S. soil.
That's because two bills recently signed by Obama -- the defense authorization and defense appropriations bills -- contained provisions barring the transfer of Guantanamo detainees into the U.S.
The White House is likely to say those transfer bans are unconstitutional, since they impede the President's ability to make military decisions as commander in chief.
But in a letter to Congress, Army Lt. Gen. William Mayville said, "Current law prohibits the use of funds to 'transfer, release, or assist in the transfer or release' of detainees from Guantanamo Bay to or within the United States."
"The Joint Staff will not take any action contrary to those restrictions," added Mayville, the director of the Joint Staff.
A U.S. official said the report from the Pentagon Tuesday will say legislative "relief" is needed from the congressional language banning Guantanamo transfers to the U.S.
If the court needs to decide who is right, it's possible the closure plan would be delayed -- potentially well past Obama's time in office.
The Republican plan
Because the Obama administration has said it could take executive action to move detainees into the U.S., Republicans have begun looking at a legal response to any such unilateral steps.
Republicans would likely cite the laws forbidding transferring detainees to the U.S. in arguing any unilateral move by Obama is illegal.
House Speaker Paul Ryan previewed the GOP strategy on Fox last month, pointing to the challenge of Obama's immigration laws as a model.
"Our border state governors who had standing in courts went and sued the administration," he said. "So what we will do, whenever he does one of these actions, is take the best way forward we can -- we can come up with to get the best result, which is to stop him from doing it."
A plan for combatting a potential order on Guantanamo could include lawsuits from the states where detainees are relocated.
Options for housing prisoners in the U.S. include the federal Supermax prison in Florence, Colorado; the military prison in Leavenworth, Kansas; and the Naval Consolidated Brig in Charleston, South Carolina, though an administration official said last week the pending closure plan would not identify a specific facility. Congress' language mandating the plan, however, calls for a location to be specified.
The attorneys general for Kansas, Colorado and South Carolina wrote in a joint letter to Obama in November that moving detainees to their states would amount to a "dangerous and illegal action that would violate federal law and harm our States."
In the letter, the attorneys general said they were continuing to "explore all legal options available to ensure the safety and security of our citizens and to enforce the rule of law."
Where will the detainees go?
State Department efforts to transfer detainees home or resettle them in a third country have steadily reduced the inmate population.
Senior State Department officials said they have already transferred 147 detainees out of the camp since 2009. Roughly one-third of them, 50, have been repatriated to their home country, while 94 detainees have been spread throughout 26 countries. Two others were sent to Italy for prosecution and one more was prosecuted in the U.S.
Lee Wolosky, the U.S. Special Envoy for Guantanamo Closure, said last month that the State Department hoped to transfer another 34 detainees already approved for release by this summer. U.S. officials told CNN the State Department has either concluded or is in the final stages of agreements with several countries to resettle all of the 34.
Officials compare the painstaking negotiations to resettle detainees to a game of chess, with Secretary of State John Kerry, and his predecessor Hillary Clinton before him, intimately involved in the discussions.
"This is hard," Wolosky said in an interview with CNN. "It's a difficult ask of the U.S. to make, to say please take these individuals whom the world has branded as terrorists. And frequently we have little to offer them in return, except the continued goodwill of the United States."
With 10 of the remaining 91 detainees expected to undergo military tribunals, that leaves another 47 detainees who could be approved by an interagency review board to be sent home or to a third country.
Last month, 10 Yemenis held at Guantanamo were released and sent to Oman. All 10 were held in U.S. custody for at least a decade without being charged. It was the largest release of prisoners at the U.S. military detention center since 2009.
Oman has taken 20 detainees who are banned from going back to their home countries, more than any other of the 25 countries that have taken in detainees.
Another four inmates were sent away earlier last month, including an inmate released to his home country of Saudi Arabia, where the U.S. has hailed the government's rehabilitation program.
More than half of the remaining detainees are Yemeni nationals. The administration is prohibited by law from transferring Guantanamo detainees back home, given the security situation in the country. Yemen is racked by civil war and home to al Qaeda in the Arabian Peninsula. Three previously released Guantanamo detainees have gone on to join AQAP since leaving the facility.
"We need to have a reliable security partner to hand over a detainee. Contrary to the perception of some, we do not just drop these guys off and say have a nice life," Wolosky said in the interview.
He continued, "We work to put in place mechanisms that are intended to keep pretty close track of them in order to mitigate any threat these resettled detainees may pose to the receiving country or the United States."
The administration has ruled against sending some detainees to their home country out of concerns they will not be treated humanely. Officials said a handful of the trickiest cases involve inmates with medical problems who cannot suitably be sent home or resettled in most countries.
Even in cases where these individuals have been approved for transfer, the inmate must approve the deal. One detainee accepted a resettlement offer and was on the plane but changed his mind before the plane took off.
A few others could be prosecuted in a third country whose nationals are counted among the inmates' victims.
For example, Jemaah Islamiah's Riduan Isamuddin, known as Hambali, has been held in Guantanamo since 2006 without being charged. He could be tried in any number of counties for his alleged role in the 2002 Bali bombings, which killed 202 people, including 88 Australians.
"There will still be diplomatic work to do, but we have changed the political context," one administration official said. "When you are talking about 60 detainees as opposed to 160, it's a different conversation."