It wouldn't be left vs right, it would be magats against everyone else. They can do domestic terrorism just fine, sure, but full blown war is a bit more on the complicated side. I seem to recall another group of racist traitors/insurrectionist who thought they'd roll the USA. Turns out wars need people, money, brains. And allies. Piss and vinegar only go so far. Who is going to help the racist, fascist side? Not Canada and Mexico, or the EU. Russia is crumbling like a good coffee cake, and China is focused on owning Asia while they still can. I can see American Ukraine War vets taking quite an interest in fighting facism at home, while it's hard for me to imagine the same crowd wanting to help Putin's orange peon.
Magats are outnumbered, live off of blue state welfare. They might start off strong, but that would not a be fight the fascists in this country would win.