I doubt even this would cause a civil war. By world standards, U.S. citizens have pretty good lives, so most people wouldn't risk it. An unprecedented and complete collapse of the U.S. quality of life would be necessary. People would need to feel like they had nothing to lose, and much to gain to attempt to fight the U.S.

I suppose a quick coup is possible. If the DoD/military backed it, I'd guess most people would just accept it as the way things are, or try to emigrate to other countries.

The U.S., the "west", and possibly the entire world is probably just destined for a long slow decline as global capitalism eats itself. Probably transitioning to something worse featuring mass surveillance, disinformation like we've never seen (powered by "AI" tech), and even greater inequality. But I'm a pessimist :)