If you take out the first part of the 2nd amendment, having to do with the well regulated militia being necessary for maintaining a free state, you kind of lose the meaning, I think....It's advising that the people, and nothing but the people, on whatever terms they deem appropriate, be the mechanism by which any encroachment on liberties, from any source, is challenged.
If there was no imperial army and the citizens of the US were tasked with organizing their own defense systems, you can't logically rule out a region having nuclear-based defenses.....It might not be realistic by the standards we're accustomed to, but it's allowed for in the 2nd amendment. "Militia," "The people" and "arms" are pretty wide open as far as how anyone might define them.
So the nuke argument is bunk. It's begging the question, eliminating citizen armies from the discussion..... An individual would never have nukes, but a regional volunteer army, equaling the army of some small country, might decide, under their leadership scheme, that it's sensible to have a nuke or two to keep enemies at bay.