Most Americans, no matter their political affiliation, do not believe that violence is a solution to domestic political divisions, according to the latest PBS NewsHour/NPR/Marist poll.
If anything happens it won't be a civil war. There is no good geological line to use as a point to start. It will be much more akin to the Troubles of Northern Ireland. Which may be honestly worse.
The biggest difference would be that there isn't an outside country that could or would step in. The US military would probably end up being divided, as many of the upper officers take oaths of loyalty to the country and constitution seriously, while a number of the enlisted people are much more partisan.
We're already seeing the beginnings of low-level terrorism, with threats of assassination against judges and other gov't officials. Mostly--almost exclusively--from the political right. It's not much of a step from there to actual violence.
Yeah, the ammo box is literally the fourth box of democracy after the soap box, the ballot box, and the jury box, but it's only to be used when the other three have failed
At the end of the day, might makes right, so we better make damn well sure the side we believe in has more of it