Canada

It’s a lot more dangerous for the US to nuke Canada than it was to nuke Japan. As for more conventional attacks, not only would a Guerilla war against people who know American culture so completely and in the Canadian landscape suck, but the Canadian military is, uh, not to be fucked with.

The Canadians fought the Germans with a long, enduring, terrible, skilful patience

-Philip Gibbs

the troops that had the worst reputation for acts of violence against prisoners were the Canadians

-Robert graves

I don’t care for the English, Scotch, French, Australians or Belgians but damn you Canadians, you take no prisoners and you kill our wounded

-unknown German colonel, as recalled by Canadian soldier Fred Hamilton

Source

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.