I'll say again, NOT! nuclear.
Iran doesn't have a button to push, north korea can't deliver a weapon more that 6k miles (out of range for US) and can't hit the broad side of a barn even at that range, russia is not interested in doing any button pushing...unless we target them.
The fallout would be international relations mainly. But I'll repeat, NOT! nuclear.
so just because america chooses not to use nuclear weapons that means other countries will do the same? america ain't stupid enough to target Russia either