American civil war feels quite possible at the moment. Even passing a budget is becoming a gargantuan governmental task subject to polarization and media trench warfare.
I think that's unrealistic. What group has both the motivation and ability to rally both state governments and a large chunk of the military into open warfare on American soil? Both parties love polarizing rhetoric to keep their base riled up, but they have nothing to gain and everything to lose in an open civil war. Various militias, "patriots," and racial and religious warriors can occupy some government buildings, kill some cops, and provoke disastrous police standoffs, but have no ability whatsoever to prosecute an actual war.