The balance of our nukes against theirs is so extreme that it's hard to imagine even a crazy man hitting us with one. Massive retaliation has been our policy for a long time and I'm sure he's aware of that. Kim needs the military to stay in power and he's mostly just keeping the military happy by giving them more armaments. The real danger is not Alaska getting the big one but in a conventional weapons attack on the south. That could kill millions. I think the essence of the problem is the Chinese want the USA out of the Korean peninsula. They see that as in their sphere of influence.