Canada

While it's possible that they've changed procedures, I seem to recall reading somewhere that after Nixon made some problematic drunken phone calls, the US arranged things so that actually launching the missiles has to go through the Joint Chiefs of Staff, not just the president. Trump may only have the safety in his grip, not the trigger.

Even if he does have the trigger, I'm betting someone would wrestle it out of his hands at that point—not because any of them give a damn about us, but because nuclear fallout in southern Ontario would likely devastate New England, given the general tendency of weather on this continent to move eastward. So you wanna have a revolution? Sending nuclear fallout in the direction of your largest population center is probably a good way to start one.