He can't declare war, even though he thinks he can as America's first dictator. Only Congress can declare war.
Yes, I have been amazed for years why we haven't sent the number of troops to protect our own border, for crying out loud. If we can send our troops (sucking many from the National Guard) to Iraq and Afghanistan, why on Earth can't we send them to stop this crap at our own border?
Executive order and police action.