It's possible to imagine using a nuke, but the scenarios are very limited.
This is actually a good reason to continue work on new weapons, particularly deep penetrators. A penetrating ground burst maximizes local fallout, but minimizes distant fallout. This is critical to actually be able to use the weapon without irradiating nearby (friendly countries, or hostile nuclear powers) nations.
Having such weapons lends credibility to the threat to use them, and increases deterrence.
Maybe we need to think along the lines of
The Moon is a Harsh Mistress 