Will Guantanamo ever be closed?

President Obama pledged just this week at his State of the Union address that he'd make good on a promise that goes back to his first day in office: shuttering the military prison in Cuba at Guantanamo Bay.

"Since I've been President, we've worked responsibly to cut the population of Gitmo in half," he said. "Now it's time to finish the job. And I will not relent in my determination to shut it down. It's not who we are."

While fulfilling that promise has eluded him, he's making good progress on emptying the facility. In the past two months, there has been a sudden surge in prisoner releases, as the administration freed more than a dozen detainees who were deemed low-level threats.

But key Republican senators, among them, South Carolina Republican Lindsey Graham, are trying to halt all transfers. He said, "To release these prisoners, given what's going on throughout the world, to me is a disconnect between reality on the ground and a campaign promise."

And it cannot be denied that some former detainees have rejoined the battlefield. For instance, Abdul Rauf, an Afghan released in 2007, recently began recruiting for ISIS, a senior Afghan intelligence source confirmed to CBS News.

U.S. intelligence says it has confirmed that some 17 percent of released prisoners have reengaged in terrorist activity since the Guantanamo detention facility was opened in 2002. But before stepping down in December, then-Special Envoy for Guantanamo closure Cliff Sloan told CBS News that that percentage is now substantially lower because vetting has improved since the detainee releases made during the Bush administration.

Asked about contacts some of these detainees later made with their terrorist associates, Sloan said that the Guantanamo detainees considered for release in the Obama administration had to undergo a "rigorous review, and the level of detainee recidivism, "of engaging in terrorist or insurgent activity, is six percent."

The White House makes two arguments for shuttering the prison--one is about cost, and another is about justice. The president said Tuesday night, "As Americans, we have a profound commitment to justice--so it makes no sense to spend three million dollars per prisoner to keep open a prison that the world condemns and terrorists use to recruit." And that cost-per-prisoner goes up every time a prisoner is released.

There are 122 detainees currently held at Guantanamo Bay. Ten have already been charged or convicted. Fifty-four have been cleared to leave Guantanamo, but the administration is still trying to find third-party host countries that will take them.

Fifty-eight of the 122 are under review as the Administration debates whether or not there is enough evidence to charge them with a crime and be prosecuted. A senior administration official told CBS News that of those remaining detainees, there are about 20-30 prisoners who are considered the hardest cases. Those are the men who cannot be charged and about whom there is "real concern" about the danger they could pose if released.

Sloan said this smaller number of prisoners can be handled by U.S. super max prisons, where the cost to house them would be only $80,000 each.

"There is no reason in the world why somebody who has been convicted at Guantanamo should not serve his sentence at a super max, very secure prison in the United States, just like hundreds of other people, convicted of very serious terrorism offenses," Sloan said.

Congress does not agree. It has banned the transfer of any Guantanamo detainee to the U.S., leaving open the question of what to do with the remaining prisoners -- particularly those considered too dangerous ever to be released.

The new Senate Armed Services Committee Chairman John McCain says he's been waiting for some time for an answer from the Obama administration about how such transfers to the U.S. could be carried out. "It's now been six years," McCain said. "Tell me what the plan is. There has never been one."

The president now has two years to figure out how to work with the Republican-led Congress to achieve a foreign policy goal that was his first and is among the most important to him.