Neither at first, I think. In the Revolution the rebels were fighting against a colonial power who had enemies that had a vested interest in a British setback, and were willing to aid them, even to the point of going to war themselves. At present it is not in my opinion likely any country would want to get involved in an internal squabble in the US- and such aid might not be accepted if offered (Neither side would be likely to accept aid from North Korea, for example.) In the Civil War the rebels were set aside by geography. We are more divided along ideology and issues than by states, although the South and some of the West would be more likely to make common cause.
If history is any teacher, it would probably more resemble something like Bosnia in the 1990s, or perhaps some of the Central Asian brawls right after the collapse of the Soviet Union. Or, from our own history, Bleeding Kansas just before the Civil War. But, one of the telltale signs the republic is fracturing hasn’t appeared yet- when the legislators start physically assaulting each other. Right before the end of Rome’s republic, the Roman senators beat Tiberius Gracchus to death, and right before our own Civil War, Senator Charles Sumner was beaten by Representative Preston Brooks. Of course, if the whole Congress has gone treasonous this sign won’t be there. But there might be yet a place for politics to work before everything becomes a set of strategic and tactical problems.
The Colonists were at the time of the Revolution subjects of the British Crown, had they lost all of the Founders would have been hunted down and hung as traitors to the Crown. Many Southerners feel the situation their ancestors rebelled against was similar to the colonists.