1) Two primary goals are to protect Seoul and prevent the firing of a nuclear or chemical-biological weapon on South Korea,Japan, and US bases in the Pacific. He has an Ohio-class submarine in place with nuclear-armed cruise missiles. That submarine will fire nukes at the mountains facing the DMZ to take out the artillery positions. Tactical nukes will hit all nuclear weapons facilities, North Korea Air Force bases and naval facilities. The other Ohio-Class submarine on patrol near North Korea with the very deadly Trident missiles will be on "ready to fire" status. Trump will got to DefCon 2. He will warn North Korea to stop now or the large and very deadly nuclear weapons will be employed.
2) All sorts of efforts will be made to kill Kim Jun Un and his management team. Massive cyber attacks will be unleashed on North Korea.
3) Trump and his management team will take cover in the shelters out in the countryside.
4) Seriously look for a declaration of marshal law from Trump.