Any talk of Civil War is fruitless without mentioning foreign intervention would immediately take over and milk the tensions forever. I've been dismissed before but what you see in third world countries is absolutely a result of foreign meddling and doing the bidding of special interests groups. America would be no exception. No way would an All Left or All Right leadership be allowed to conquer the continent and usher in stability. Russia, China, Israel, Iran, hell, get all of America's enemies in one room and watch as they play America like it's some sort of board game and hand out firearms like crazy to any rebel group that wants it. It's a scenario that benefits no one but those with gun contracts.

Edit: And America is so interconnected with the world that Civil War might as well be World War. Taiwan, South Korea and Japan cannot afford to watch their military protectors go on hiatus, since that spells China invading their nations with zero repercussions.