I would guess the world would just implode. The reason I think that is because after such an attack, the US would have to be either attacked by various world powers or continue attacking further. If they manage to take take enough of the world over and overthrow enough governments, they would have to install puppet governments like we did in Afghanistan, Iraq, etc. Since only a right-wing administration would use a nuclear tactic, especially unprovoked, the puppet governments would also be right. They would attempt to export American conservatism out to other countries, and it would go unchecked since there is no one to check them. Thus greed, ignorance, closed-mindeness and everything else that comes with labels such as "Republican", "right-wing" and "Christian" would spread, and the world, like I said in the beginning of the post, would implode.