Several news sources are reporting that Trump's "fire and fury" statement was improvised.

"If that is true, we have no moderating influences between Trump and the nuclear button."
I don't don't know how the "nuclear football" works, except that it is a heavy briefcase containing a series of options and an electronic confirmation process.
I don't think the president presses a button and the missiles and bombers start flying to their targets.
I have to believe Congress and/or the military has pondered what happens if a president's marbles suddenly slide off the plate and s/he orders an unprovoked strike. If so, there may indeed be an intermediary who would have to give the final confirmation code.