This is a very nasty situation with no way to win it without cost and the cost is going to be to innocent bystanders in S.Korea and Japan. Someone needs to take Kim Jong Un "out." The next step might be a full naval blockade of N. Korea as was done to Cuba. The only things getting in an out would be through China and the Chinese would need to be persuaded to cut N.Korea off. That kind of pressure might provoke an internal coup.