Any sort of conventional attack on North Korea would be sheer lunacy.
Trump has already attacked Syria a number of times. That is Nazi like aggressive war and is banned by the Geneva Conventions. He has ramped up the war in Yemen. He has urged on Saudis in their war against the Shia of Arabia, now a full-blown insurgency. Trump has been menacingly threatening Iran. Trump is now threatening to invade and conquer Venezuela.
Trump cannot attack North Korea in any way, shape or form unless or until they launch an attack on us.
Preventive war is always illegal in all contexts. Preventive war is what the Nazis and Japanese engaged in. All wars of aggression are staged as preventive wars. Preventive war is outlawed at the Geneva Conventions. Many Germans and Japanese were executed for waging preventive war.
Pre-emptive war is legal, but you have to have excellent evidence that the other country is going to attack you and is about ready to do so in the very near future. The pre-emptive war championed by the US is almost never the actual pre-emptive war that is actually legal.
There is no sense in saying anymore that Trump is never going to attack anyone.