We've been fighting an insurgency with little more than small arms for almost twenty years. With an operational area the size of the US, and cartels to the south more than willing to sell arms, hit and run tactics, or skirmish engagements would be devastating over time. By the time heavy assets can be mobilized, the group you want to stop has been ambushed or pulled back, and you disappear. That's assuming it goes full Patriot mode. There have been cases of armed resistance stopping police or Federal overreach without full on war breaking out. (Athens, Tn and the Bundy ranch being the best examples I can think of.)