It will be a guerrilla war. And asymmetrical. In fact, knowledge of effective use of terror would be essential.
I agree with you. Since there is no geographic line that defines the sides (ala CW I), the combatants will be mixed together in all locations. It would be difficult to define the enemy. The best the combatants can do is to take out the leadership of the other side as they are well defined.
But honestly, I can not see how the whole thing comes about. I do not see a possible moment that is Lexington or Concord.
Only on the coasts. In the heartland the leftist will be rounded up post haste. My guess in the middle of the US the leftest won't even make peep. Governors will take over and it will be business as usual.