"Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States or any place subject to their jurisdiction."
Thirteenth Amendment, passed in 1865 as part of the conclusion of the Civil War.
The inmates of Gitmo are not criminals, they are enemy soldiers, captured upon the battlefields of Afghanistan. They have not been duly convicted of anything. An overpaid army of lawyers, working their cases since 2001, has been unable to convince an American court or court-martial to convict them. Under American law bearing arms against the United States is not a crime.
And under the 13th Amendment, if they ain't convicted, we cannot hold them in jail.
The Bush Administration understood this, and decided to put these people in Gitmo, in the hopes that being off shore, US judges would be less likely to order the prisoners released.
And today, Obama engaging in some favorite magical thinking, wants to close Gitmo and transfer the remaining inmates to somewhere inside the US.
He is gonna encounter a good deal of resistance.