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President Barack Obama on Tuesday presented a long-awaited plan to Congress to shut down the detention facility at Guantanamo Bay, insisting that keeping the prison open is "contrary to our values."

"It's been clear that the detention center at Guantanamo Bay does not advance our national security," Obama said from the Roosevelt Room at the White House. "It undermines it."

The plan, which has been on Obama's agenda since he took office in 2009, hinges on the transfer of between 30 and 60 detainees to U.S. soil, and suggests several possible locations in South Carolina, Kansas and Colorado. The rest of the 91 detainees at the prison could be sent to other countries.

Related: Two Guantanamo Bay Detainees Headed to Ghana

There are currently 35 detainees eligible for transfer and the plan calls for an accelerated review of remaining detainees to determine whether they pose a threat — and, if not, if they should be eligible for transfer.

"Keeping this facility open is contrary to our values," Obama said. "It undermines our standing in the world. It is viewed as a stain on our broader record of upholding the highest standards of rule of law."

Obama is already facing pushback from Republicans in Congress. Both chambers have repeatedly passed legislation banning any effort to move detainees to the U.S.

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“President Obama seems to be captured on one matter by one campaign promise he made in 2008,” Senate Majority Leader Mitch McConnell, R-Ky., said on the Senate floor on Tuesday.

“This isn’t even a case where the president can use some kind of pen and phone strategy by claiming the Congress refused to act,” McConnell said.

Rep. Mac Thornberry, R-Texas, chairman of House Armed Services Committee, has said his panel would hold a hearing on a closure plan. But he sent a letter to Obama warning that Congress has made clear what details must be included in any plan and that anything less than that would be unacceptable.

Related: Senate Bill Passes to Ban Guantanamo Bay Detainees From U.S.

Obama said politics has complicated an issue which once had bipartisan agreement.

“When I first ran for president, it was widely recognized the facility needed to close,” Obama said, adding that former president George W. Bush and former Republican presidential candidate Sen. John McCain, R-Ariz., once backed closure.

But such plans became unpopular, Obama said.

“Suddenly, many of those who said it needed to close backed off because they were worried about the politics,” he said.

“I think a lot of the American public are worried about terrorism, and in their mind the notion of having terrorists held in the United States rather than in some distant place can be scary,” he said. “But part of my message to the American people here is we’re already holding a bunch of really dangerous terrorists here in the United States because we threw the book at them. And there have been no incidents.”

The White House hasn’t officially ruled out the possibility of the president using executive action to close Guantanamo Bay prison if an agreement with Congress isn’t struck.

U.S. officials say the plan considers 13 different locations in the U.S., including seven existing prison facilities in Colorado, South Carolina and Kansas, as well as six other locations on current military bases. They say the plan doesn't recommend a preferred site and the cost estimates are meant to provide a starting point for a conversation with Congress.

Some lawmakers representing South Carolina, Kansas and Colorado have already made it clear they oppose housing Guantanamo detainees in their states.

Related: Guantanamo Bay: Who Are the Detainees Left the Prison Facility?

Obama, for his part, called for immediate action.

"I don’t want to pass this problem on to the next president, whoever that is," he said.