During times of unrest, stuff happens. Are they average citizens, thugs, rebels or the enemy? Depends on your POV.

Fortunately, the US has strong institutions and balance of powers that make civil unrest, etc a rare event. When there is, actions depend on the situation.

Note that I'm not an advocate of arming one's self against the government in any way. I'm pointing out that the fantasyland of some citizen militia fighting any modern nation-state is absurd.

Examples of things where unrest or rebellion were put down by force:

https://en.wikipedia.org/wiki/Kent_State_shootings

https://en.wikipedia.org/wiki/Whiskey_Rebellion

https://en.wikipedia.org/wiki/Nat_Turner%27s_slave_rebellion

https://en.wikipedia.org/wiki/New_York_City_draft_riots

https://en.wikipedia.org/wiki/Coal_Wars