All the countries most likely to use a nuke as a first strike or terrorist weapon only have or can get 1 or 2 operational nukes.

Personally, my policy recommendation is for the U.S. to declare any first strike use of nukes against any country will result in the nuclear obliteration of the offending country. (I'd have suggested the U.N. Big 5 but that group (and the U.N. as a whole) couldn't organize a an office party amongst themselves, much less be trusted with the security of the world.) We don't have the be the policemen on the world, but on that issue we should grab the minotaur by the horns.

And you use nukes whith high thermal and blast in that case that are detonated as high air bursts to minimize radioactivity. Neutron bombs would be ideal. Point is, we'd probably only have to do it once, and all those petty, tinpot madmen running totalitarian state would get the message. And we'd have eliminated the worst of the bunch.