I doubt we’ll do anything to stop him. I just don’t think America has the stomach for that kind of thing any more.
Depends, are we willing to risk major land war? Can we take them out with air power and maybe a limited ground incursion? If that is a viable option I look for an eventual attack. A full on ground invasion makes it a more dicey option.
The other option is to accept NK’s nuke and practice a bastardized version of MAD with them to an extent since we have a limited ABM ability. This option would of course cause Japan and South Korea to go nuclear fairly quickly.