Bush did it because the government was sued by Eric Holder’s lawfirm, and was forced to transfer this guy - to a stable country whose dictator had been intimidated by us.
Obama and the “Al-Qaida Spring” changed all that, and that’s what led to his release.
If that's the story (Bush was forced to do it), all fingers can point to Holder.
I don't see a downside.
So what number is this guy? I know there have been numerous former Club Gitmo members who have gone on to bigger and better jihad.