(CNN) If President-elect Donald Trump decides to make good on his campaign pledge to "load up" the prison camp in Guantanamo Bay, Cuba, with new domestic terror suspects caught in the US -- including American citizens -- legal experts say he is asking for an unprecedented constitutional showdown.

Voters first received a peek at Trump's stance on Guantanamo Bay back in 2015 when talking points on various policy questions were leaked ahead of a Republican debate. On the issue of whether he would close the detention facility, the memo stated: "No. I would also take away the passports of Americans who fight for ISIS and send them to Gitmo for some R&R."

On the campaign trail in February he railed against President Barack Obama's promise to close the facility -- vowing to fill it up with additional detainees.

"This morning, I watched President Obama talking about Gitmo, right, Guantanamo Bay, which by the way, which by the way, we are keeping open. Which we are keeping open ... and we're gonna load it up with some bad dudes, believe me, we're gonna load it up," Trump told the crowd.

Trump went a step further in August, telling The Miami Herald he would be "fine" trying US citizens suspected of terrorism in military commissions.

Who can go to Guantanamo?

As the President-elect makes the transition from campaigning to governing, the real question will soon become: who exactly is even eligible for transfer to Guantanamo?

Legal experts on both sides of the political aisle agree that Trump's options are limited in light of the congressional authority currently available to detain someone.

The Authorization for Use of Military Force (AUMF) authorizes the president to use force against those who "planned, authorized, committed, or aided the terrorist attacks that occurred on September 11, 2001, or harbored such organizations or persons."

Under the Bush and Obama administrations, the AUMF has been used to justify efforts against al Qaeda, the Taliban, and other associated forces (including, more controversially, ISIS).

But neither President Bush nor Obama ever sought to use the AUMF to detain someone at Guantanamo who was captured in the US.

Jonathan Hafetz -- a professor at Seton Hall Law School who has represented numerous Guantanamo prisoners in federal court -- said that is precisely what makes Trump's statements on sending American ISIS-supporters to Guantanamo so extraordinary.

"To bring anyone from the US -- citizen or not -- to Guantanamo and put them in military detention would be unprecedented," Hafetz said. "Even the Bush administration, in its most sweeping views of executive power, didn't transfer (terror suspects arrested in the US) to Guantanamo."

So what would stop Trump?

As an initial matter, "there are a lot of people who are not covered by the AUMF," explained Benjamin Wittes, editor-in-chief of the national security blog, Lawfare, and a senior fellow at the Brookings Institution, told CNN.

"When you look at a self-radicalized person in Florida who declares his allegiance to ISIS, can you say he is under detention authority? Not even close," Wittes added.

Professor Matthew Waxman of Columbia Law School, who served in the Department of Defense overseeing detainee policies under the Bush administration, explained that "the government to date has been relying on perhaps a plausible, but very stretched, interpretation of the AUMF to include ISIS (for purposes of drone strikes)," and the concept of further relying on the AUMF to detain ISIS-supporters not captured on the battlefield, but arrested in the US, would be a "big stretch."

"We've come a point where federal courts may say AUMF has lapsed. ...The practical circumstances on the ground are too different at this point from the aftermath of September 11th for the AUMF to continue to provide legal authority to detain anyone at Guantanamo. ...It's not 2004 anymore," said Wells Dixon, a senior staff attorney at the Center for Constitutional Rights, who has also represented several detainees at Guantanamo.

As a result, the concept of sending an ISIS-inspired, lone wolf attacker caught on US soil -- such the Pulse nightclub shooter in Orlando, or any one of the numerous individuals the US Justice Department has charged with providing material support to ISIS over the past several years -- to Guantanamo would almost certainly trigger an immediate legal challenge, especially since the US Supreme Court has never had an opportunity to squarely address such a scenario.

But the prospect of lengthy litigation could undermine Trump's own goals by inviting greater judicial scrutiny of the detainee program as a whole -- not to mention the fact that he could lose a court fight and the suspect would walk.

"People think it's a tough guy move (to send someone to Guantanamo), but you end up with lots of litigation opportunities," Wittes said.

"It's not as much that Trump is going to run up against clear legal barriers or prohibitions to what he wants to do, rather he's going to be advised that there are a whole set of legal complexities that make doing it risky, problematic, costly or impractical," added Waxman.

But Harvard Law Professor Jack Goldsmith -- who served as assistant attorney general in the Office of Legal Counsel under President George W. Bush -- suggested on Lawfare in November that the very likelihood of swift court challenges, and possible Supreme Court review, should appease liberals' handwringing about Trump's potential for executive overreach.

"Chest-thumping about expanding presidential power was self-defeating in the Bush administration and will be more so in the Trump administration," Goldsmith said.

'This is harder than you'd think'

Chest-thumping or not, when asked whether Trump's views on Guantanamo had changed since the campaign, a Trump transition official speaking on the condition of anonymity suggested Trump's views remain unchanged, and pointed to Congress' prohibition on using funds to transfer Guantanamo prisoners to the US.

National security experts outside of Trump's inner circle, however, said he will face a different reality once he becomes president and discover the unique challenges posed by Guantanamo.

Cully Stimson, who served as the deputy assistant secretary of defense for detainee affairs under President George W. Bush, emphasized the "big learning curve" for any new president absorbing difficult national security issues, but suggested the situation at Guantanamo is particularly fraught from both a legal and policy perspective.

"This is harder than you'd think," Stimson told CNN.

As a result, some speculate that notwithstanding his hardline campaign statements, Trump will ultimately take the path of least resistance and simply rescind Obama's executive order closing Guantanamo, without actually adding to the detainee population.

Trump's pick for attorney general, Sen. Jeff Sessions, has said that it would be a "terrible mistake" to close it, and Rep. Mike Pompeo, his nominee for CIA director, has a page on his website that says keeping the prison open is "the right option for American national security."

But the mere refusal to shutter Guantanamo's doors provides little comfort to the advocates who have been representing detainees there for close to 15 years.

"He is going to find that it is a lot harder to keep it open than he might think," said Dixon, but "certainly if he does try that, he will be met with fierce opposition."