Nukes are only effective against cities and concentrated assets, red states are too far dispersed with few concentrated assets that would require a nuclear strike.
The blue areas are vulnerable, it's enough for an attacking force to start a firestorm in one of those heavy blue areas all full of closely packed wooden houses.
Something as stupid and simple as a few hundred flaming arrows, or even modified chinese rockets (fireworks) and blocked streets/firehouses would wreak havoc, never mind nukes. Look at what happened by accident in Philadelphia with a single flash bang (or couple?) the cops used against MOVE. This happened in 1985 and the cops accidentally burned down some 65 homes without trying, not through malice but rather stupidity. A malicious group could do far worse.
Imagine if someone really wanted to go after those concentrated blue city populations... say they started a few firestorms and disabled the firehouses and water mains? Hopefully, it never comes to that.
The rebels would be wise not to wait for the Federales, but to go after them in their homes - sort of as if the Jews were able to escape the ghetto and go after the Wehrmacht on their holidays in their homes. Outside the box.
Government employees have special license plates, they live in well known areas... it is easier to find them than them to find the rebels.
The enemies of freedom and promotors of statism are concentrated in cities. The defenders of freedom and the constitution are widely dispersed.
Just like if Russia and the USA ever exchanged nukes, the Russians would have been doing us a favor taking out our worst ghettos... Detroit, Baltimore, Newark, DC, etc. - granted, there are lots of good people there too, but those are largely gutted, pillaged sewers by and large - whereas in Russia, the cities are where the intellectuals live and are prosperous while the oblasts are full of drunken, toothless, tuberculosis ridden alcoholics.
Hopefully, it will never come to such blows, but if it does, I would rather be in a red area than a blue one, wouldn't you?
Of course, it's all just armchair strategizing, I have no intention of shooting my fellow citizens as an aggressor - nor anyone else for that matter.