There are various groups, some of which tend to be highly geographically-clustered, with fairly high levels of trust of their own "team." And weapons are readily available to speed a transition to enforcement-by-the-local-majority vs enforcement-by-other-bodies (higher-level state or federal government).
Breakdown of governance -> authoritarianism is a common sequence regardless of political lean of the new regime; and both sides think there's currently a breakdown of governance somewhere in the country. If you're Democrat-leaning, you'd read that as red states, of course, but even on the flip side: to some pundits places like SF are already starting to turn into a violent anarchy; a new, armed, local authority would be a logical followup step emerging out of that, sorta Mafia-style.
I don't think this is likely - I don't think today's crises are unprecedented compared to the 1960s/70s or various earlier periods of American unrest - but there's nothing innate about America that would prevent it, and there are plenty of historical American examples of those in power using force to strictly control others.