If these people are "the worst of the worst" then we already have infrastructure to deal with that. Gitmo is for extrajudicial punishment that should have been outlawed decades ago. "Thanks Obama"
Obama had a campaign promise to close Gitmo and then didn't. It was made difficult by Republicans, but it was still just sort of abandoned because it would have cost political capital and they didn't want to have that fight.
But he did take it from a couple hundred prisoners down to about 50. Of those 50, something like 20 were cleared for release, and the remaining 30 were going to trial for various terrorism charges (helping plan 9/11, for example).