Further to Ben's points on Senators Ayotte and Graham, note that the latter suggests that the Administration did something improper, in its handling of Sulaiman Abu Ghaith:
“To bring this person to New York City, if that's what happened, without letting Congress know is a very bad precedent to set,” Graham said. “The Congress has tried to tell the administration that when it comes to people like this we want them to go to Gitmo to be held for interrogation purposes.”
In fact, Congress hasn't done that. Despite several rounds of detention legislation, nothing in existing law---zilch---obligated the Administration to notify Congress, in advance, of its plan to bring Ghaith from Jordan to the United States; or, much less, to opt for interrogation and prosecution at Guantanamo. To the contrary, current law specifically preserved the criminal justice system as an option in Ghaith's case. Of course, if it genuinely wishes to impose even more strictures on the President's detention authority, Congress can "try to tell the administration" to insist upon Guantanamo in cases like these. But it just hasn't done so yet---and that's a good thing, for the reasons that Ben and Bobby described, among others.
In the meantime, what's with the congressional grumbling about the President's exercise of authority which Congress actually has granted him? Recall that when Warsame was transferred to civilian custody, Republicans in Congress attacked the move as "directly contradict[ing] pending legislation." But Warsame's transfer didn't offend any then-existing rules, just as Ghaith's doesn't offend any current rules, either.