When the Nazis took over Germany, there was no civil war. There was not sufficient organized resistance to qualify as a civil war.
In the USA, there are a few possibilities:
* Somehow fair-ish elections are held that are capable of rejecting the Republicans; we get another shot at resolving issues through existing institutions (didn't go well last time)
* Mass uprisings result in a largely peaceful new government
* Civil war
* Total capitulation to fascism
Which will it be?