Well, I don't think it's the goal of the American President to change the regime. It's the goal of the American President to stop North Korea from having an ICBM that can hit America with a nuclear weapon on top. He would go to war to prevent that. That's where war would be likely to occur if they continue to threaten the homeland.
I hope diplomacy will work. We got two bad options. That is to let them get a missile to hit America, or go to war to stop them. China should have two bad options. Deal with a nut job in your back yard, or realize that there will be a war in your back yard.