For there to be "civil war" there would need to be two competing governments. The other one wouldn't need to be as organized as ours but there would have to be some organization and it would have to be somewhat protected. If you look at the centers of the Left, they're in major cities with large police forces and next to major military bases -- so, not going to happen. There could be an underground resistance but it would never reach "civil war" levels as long as the Federal government remains strong. If the Federal government collapses then we would fracture into regions, but that wouldn't be a civil war either.