A guard walks into the Guantanamo Bay Detention Center, also known as "Gitmo", a maximum security detention center at the U.S. Naval Station at Guantanamo Bay, Cuba on Oct. 22, 2016.

The U.S. military's Joint Task Force Guantanamo is still holding 60 detainees at the prison, down from a previous total of 780, including 20 cleared for release.

On his second day in office in 2008 President Obama issued an executive order to close the prison, which has failed because of political opposition in the U.S. Congress, mostly from Republicans who argue that they won't jeopardize national security over a campaign promise.