In a terse letter to leaders on Capitol Hill, Obama said “there is simply no justification beyond politics for the Congress’ insistence on keeping the facility open.”

“Members of Congress who obstruct efforts to close the facility, given the stakes involved for our security, have abdicated their responsibility to the American people,” he added. “They have placed politics above the ongoing costs to taxpayers, our relationships with our allies, and the threat posed to U.S. national security by leaving open a facility that governments around the world condemn and which hinders rather than helps our fight against terrorism.”

Thursday evening, the Pentagon announced the final four Guantanamo transfers of the Obama administration with just hours remaining in his presidency, sending one detainee to Saudi Arabia and three to the United Arab Emirates.

The Obama administration has transferred as many inmates as practical to the custody of foreign countries after reviewing their cases — for a total of 196, including more than 50 in the past year, according to a White House fact sheet.

Republicans have criticized those transfers, accusing Obama of trying to fulfill his campaign promise at the risk of detainees reverting back to terrorism. As many as 30 percent of detainees who have been released have been confirmed or are suspected of re-entering the terrorism fight.

But Obama argues that most of those were released during the administration of President George W. Bush.

“For detainees transferred since 2009, less than six percent of former detainees have been confirmed by the Intelligence Community of engaging or reengaging in terrorist activity, and less than seven percent of former detainees are suspected of reengaging in such activity,” Obama wrote.

Most frustrating to Obama, Congress has repeatedly prevented him from moving the remaining detainees — considered the most dangerous — to maximum security prisons on American soil.

“The restrictions imposed by the Congress that prevent us from imprisoning detainees — even to prosecute and secure a life sentence — in the United States make no sense,” Obama wrote. “No person has ever escaped one of our super-max or military prisons here, ever.”

Human rights advocates have pressed Obama to use his executive powers to close the prison unilaterally but he has opted not to try to circumvent the legislative restrictions.

President-elect Donald Trump, meanwhile, has vowed to keep the prison open. It is unclear if he intends to hold additional suspected terrorists there.