In 2008, one of US president Barack Obama's campaign promises was to close the US government's prison facility in Guantanamo Bay, Cuba. It's still open. He blames congressional (and sometimes specifically Republican) obstructionism for that. But now that he's on the way out, there's a nuclear option.
It is possible that he does not have the executive authority to close the prison against the will of Congress.
It is possible that he does not have the executive authority to move the prisoners at Gitmo to other facilities (facilities actually in the US, where the fiction that constitutional protections don't apply to them would be less tenable) against the will of Congress.
But Congress has no say whatsoever regarding who he might choose to pardon.
If I was Obama and I really wanted to shut down the place, I'd invite Mitch McConnell and Paul Ryan over for a chat. And that chat would be an ultimatum:
"You can let me close the place, and the people you consider most dangerous will be transferred to mainland facilities. Or I can just pardon every last prisoner there and you can continue to run an empty prison and take the blame for the guys you could have kept behind bars walking free instead. Let me know. You have 72 hours."