Trump doesn't have a Big Red Button. There's a whole command and control infrastructure between the President and a nuclear launch. I doubt he'd even be allowed to get the codes out the Nuclear Football.

Someone will come along and argue the the military allowed Trump to start an illegal war and kidnapped a head of state. Put together, those pale in comparison to the consequences of even a small, tactical detonation. I can't even begin outlining the events that would follow.