He is neither crazy nor a psychopath, he's just a run of the mill small time dictator who's figured out a way to grab some headlines. Best thing the US can do is ignore the hell out of him. There is nothing he can do to the US, let his neighbors China, Russia and South Korea worry about him.
Squeeze couple of B dollars with blackmailing from US seem like an attractive proposition. But sure he got worried about coming devaluation of USD so things got in a fast lane.