Suspicions are mounting on Capitol Hill that President Obama could try to use executive action to close the Guantanamo Bay detention center, even after Congress this week approved legislation that would keep the facility open. 

The defense policy bill approved Tuesday would bar the transfer of Guantanamo inmates to the United States. Obama, despite opposing that provision, plans to sign the bill. 

But the White House may have a back-up plan. Press Secretary Josh Earnest has indicated twice in recent days that Obama could use executive action to get around Congress.   

“I'm going to protect the ability of the president to use his authority [to] move the country in the direction that he believes it should be headed, and particularly when it comes to an issue like … closing the prison at Guantanamo Bay,” Earnest said after the Senate vote, declining to rule out the use of executive action. 

Obama still is trying to fulfill his 2008 campaign promise to close the facility, with just 13 months remaining in his presidency.

To date, his efforts repeatedly have been thwarted by Congress, particularly by Republicans who argue that bringing known terrorists onto U.S. soil for trials and prison terms is too much of a national security risk.

The facility at the U.S. naval base in Guantanamo Bay, Cuba, was opened in the wake of Sept. 11, 2001, terror attacks as an expedient move to get terrorists off the battlefield. But the president argues that keeping the 112 detainees remaining in the facility -- including some who have never had a trial -- is unjust and expensive. 

Congress and the administration continue to move in opposing directions on the issue. The $607 billion defense policy bill that banned moving detainees to the United States was approved days after the administration acknowledged the Pentagon is set to release a report on the pros and cons for three potential U.S. detainee-transfer facilities. 

While leaving the door open for executive action, the president showed little interest in trying to veto the defense bill, considering the 91-3 Senate vote and 370-58 House vote last week -- numbers that indicate Congress has enough votes for a veto override.

In recent years, including fiscal 2014, Obama signed the bill with a statement objecting to similar Guantanamo restraints.

Even Texas GOP Rep. Mike McCaul acknowledged -- after Earnest first mentioned executive action -- that Congress may have little redress on executive action and called on Americans to mobilize.

“It's hard to stop this kind of action,” McCaul, chairman of the House Committee on Homeland Security, told “Fox News Sunday.” “I would hope the American people would rise up in numbers so strongly … that [Obama] will decide to back down.”

He expressed particular concern about bringing the “worst of the worst” detainees into the country.

“You're going to see a heightened terror-alert threat in the United States,” McCaul said. “It would be highly reckless and irresponsible.” 

Even if Congress may be unable to act, a bid to use executive authority is likely to bring accusations of government overreach and lawsuits from other quarters, as with Obama’s 2014 executive actions on immigration.

The actions -- to provide work visas and delay deportation for millions of illegal immigrants -- were again blocked as a result of a federal appeals court decision this week. And the case could be headed to the Supreme Court.

Whether states that receive detainees or others would have legal standing to challenge executive action on Guantanamo is unclear because there is no legal precedent.

However, Charles “Cully” Stimson, a Heritage Foundation legal scholar, pointed out Wednesday that plaintiffs must show “injury” or harm for a court to say they have legal standing to proceed with a case and that a taxpayer suit or one by a local sheriff on Guantanamo is unlikely.

“All of those people are unlikely to have standing,” he said.

Stimson thinks that Congress has perhaps the best chance to achieve standing, consider the suit filed last year by House Republicans arguing Obama acted illegally in implementing his Affordable Care Act.

The suit was authorized after the House passed a resolution and filed it in a U.S. District Court, a move Stimson thinks Congress  could follow if Obama indeed uses executive action on Guantanamo.

However, Republican lawmakers in South Carolina, one of the three states in the pending Pentagon report, appear willing to mount a legal challenge.

“We are absolutely drawing a line that we are not going to allow any terrorists to come into South Carolina,” Gov. Nikki Haley said in a news conference this summer. “We’re not going to allow that kind of threat.”

Haley is joined Sen. Lindsey Graham and Rep. Mark Sanford in opposition to detainees coming to a naval brig near Charleston.

The other two states in the Pentagon report are Colorado and Kansas.

GOP Kansas Sen. Pat Roberts touts having since 2009 kept detainees out of the corrections facility in Leavenworth by holding up Senate confirmation on Obama nominees.

On Tuesday, Roberts launched an online petition for Americans to express their opposition to Obama using executive action.

“Relocating terrorists to the mainland will paint a target on the American communities forced to house these detainees,” Roberts said. “The president has proven he will act in the absence of congressional action to fulfill his campaign promises.”