Sectarian violence from the right isn't really a concern, not after Waco, Ruby Ridge, and Charrlottesville. A couple of Po'Boys may rough up some dangerhairs, but that'll be it.
I do worry about the radical left going full ape mode and unleashing a chimpout to end all chimpouts should Biden be called out for fraud and lose. An low-intensity asymmetric conflict is on the table if the Democrats' leftist allies feel they've been cheated two times running. As can be seen in this thread, civic disillusionment is a real phenomenon that can and will happen if the integrity of the Republic's elections are dubious in any way. While the right may have a stark majority of the private arms in this nation, the left has an almost religious zeal behind them that compels them to risk it all for the Right Side of History™. A man(child) with nothing to lose is truly a dangerous thing.