Thing is with the US military these days is that the leadership isn’t filled with hawkish drones ready to follow any obscene order from the President. They are very conscious about Trump and politically aware. I doubt they’d approve of any preemptive strike of any kind against North Korea unless the US had been very seriously directly threatened with a tangible threat.
I think if tensions do increase the joint chiefs would put pressure on congress to assert their authority.
He happy to escalate US involvement in Syria and Afghanistan because it’s comparatively low risk and he appears he’s dealing with radical islamists at the source, a move with his supporters in mind but beyond sendings a task fleet to that part of the world he’s done no real action against NK. Politically he scores points with his base with his defamatory rhetoric against NK and their leadership, he appears tough on NK but I think Trump wants to frame any actual action against North Korea as a Chinese lead decision.
Since WW2 the US have always sought international cooperation as some sort of approval for their military actions. They’re extremely unlikely to do anything solely on their own
Generally I think people overestimate NK nuclear capabilities/potential