The US had nukes in Vietnam and still lost. The use of one nuke against American citizens would result in an overthrow of the government and war crimes trials for all responsible.
We had the threat of Russians using nukes on us during Vietnam. With the very big threat of someone else like Russia and/or China nuking us, the worst thing we could ever do is show ano insane willingness to use them. Plus, even the Russians didn’t nuke Chechnya or Afghanistan, so it goes to show that they are deterred from using them even if the immediate Enya can’t fight back.