This has been discussed at length:

USGOV will never use nukes against Americans, if they did, Russia / China / whoever would join in to "liberate the American people".

USGOV is fabulously under-powered for fighting a civil war. Dems are concentrated in death-trap cities, mountain-rednecks are spread out, self-sufficient, basically been preparing for generations for this.

Infrastructure: Electricity, water, bridges... Snip -> lights out.