I think the possibility of a revolution is way higher than that of a civil war. The problem with civil war is that there aren't clear lines to split upon. Texas has a lot of Democrats, and California has a lot of Republicans, and there's no easy way to tell who is who. And in the case of a civil war, the US military would /HAVE/ to get involved, and the majority of it is likely to side with whatever group of people didn't start firing first. Plus the rallying points are weak at the moment. Democrats may have voted for Clinton, but none I know liked her enough to die for her. And while there's a very very loud group of diehard Trump fans, there's a whole lot of Republicans who aren't too keen on him either and wouldn't follow him into a civil war.
Poor vs rich is a more plausible scenario. The military is harder to predict in that case, a LOT of the military comes from poorer families, and they're not going to be eager to shoot their own parents or siblings. Much of it would probably just sit it out, since it's a no-win scenario for them. But even then, for that to happen there has to be enough people who believe that the future for their families is /so/ bleak that dying for the chance at better is acceptable. The quality of life for most of the poor in the US simply isn't that horrible yet in most places. It's been headed that direction perhaps, but it'd still take a fairly major trigger event to push it over the edge.