Well, we just lived through 8-years an illegal President giving many illegal orders. ("illegal"="unconstitutional").
In terms of the President's Constitutional responsibilities, the question here comes down to whether he determines, with clear evidence, that NK must be preempted.
The troll neverTrumpers here and the demoncrats everywhere are trying to imply DT would OR could nuke NK on a whim. Sheer BS.
The only legitimate "whim" target for a nuke might be DC.
We’re not going to preemptively nuke NK to rid them of nukes than Israel would have nuked Osirak to remove their capability at that time. The preemptive strike was and would be conventional.
Again, based on the facts and the advice of the military advisors the president will authorize military action. If not reacting to a validated nuclear strike attempt; the response will not be nuclear.