Most constitutional scholars would agree the ability to close the prison at Guantanamo Bay, Cuba, has always rested solely in President Obama's hands. As the commander-in-chief of the U.S. military, Obama simply doesn't need Congress's approval to shut down the military prison.

But for reasons still being debated in these circles, Obama has waited long enough to act that political opposition to the idea has built so much that, today, it's quite possible he missed his window altogether — at least if he wants to avoid total political upheaval.

All of which means that, as Obama asks Congress for a final time to help him out, he is more likely than not to leave office with one of his signature campaign promises unfulfilled.

Recall if you will that, in January 2009, a freshly inaugurated Obama signed an executive order directing the prison be closed in a year. He set up a force to help him come up with a plan of what to do with the remaining 245 or so prisoners.

Almost immediately, said Cornell Law professor Joseph Margulies, the conservative media started to cry foul at the idea. What had been a rallying point among a political left that was alarmed by allegations of torture there under the Bush administration became a rallying point on the right. Conservatives were alarmed this new president would mishandle such a matter of national security.

Obama's self-imposed January 2010 deadline to close Guantanamo came and went. Closing the facility, he told reporters in November 2009, is "also just technically hard." Next year it would shutter, he predicted.

But as time went on, it got much more difficult for Obama to act. Republicans in Congress who were concerned the president didn't really have a plan joined with enough Senate Democrats concerned about where these prisoners would go and put up a roadblock. They used their leverage and the power of the purse to pass legislation preventing Obama from spending even a nickel to move detainees to the United States for detention and trial.

That's largely where the battle lines stayed over the years. As Obama spent seven years trying to craft a consensus plan to shut down the prison — the most detailed of which he announced Tuesday morning — the opposition spent seven years rallying politicians and Americans to oppose it.

Today, Obama's plan to move some detainees to the United States is DOA in the Republican-controlled Congress, as underscored by this tweeted reaction from Sen. Pat Roberts (R-Kan.):

Experts think Obama won't move the remaining 90 or so prisoners here over Congress's objections. Doing so would almost certainly welcome lawsuits from Congress, said Jim Cohen, a law professor at Fordham University, and even criticism from many Democrats. So Obama is stuck on what to do about Guantanamo.

Margulies thinks the most likely outcome is that Obama and his team whittle down the detainees the best they can, and in the end he leaves two- or three-dozen languishing in Cuba for the next president to deal with.

It's not perfect, but Obama can argue that, of the 800ish prisoners who have ever been held there — and the 245 or so who were there when he came into office — leaving with just three-dozen ain't bad.

"He can say, 'It took me a hell of a lot longer than I wanted, but I did the best I could and I got rid of a lot of the guys I should have gotten rid of,' " he said.

But Obama most likely will never be able to say what he's wanted to say for almost eight years now: that he closed Guantanamo Bay prison for good. And even he has admitted that he simply waited too long.

"The politics of it got tough, and people got scared by the rhetoric around it," he said in March last year. "Once that set in, the path of least resistance was to leave it open, even though it is not who we are as a country."

Reasonable people can debate that past point, but Obama's political analysis here is spot-on.