In the event of a tyrannical US takeover…I mean it depends on what kind of Tyranny. The most likely would be a sort of fascist tyranny with flavors of a Christian theocracy. In that event, even if there was no rebellion, a fascist US would crumble and burn with a few decades. Fascists absolutely suck at managing a state for a myriad of reasons. Check out UR Fascism to see what I mean, basically Fascism is one big case of “My feelings don’t care about these facts” but on a governmental level.
The only way a rebellion would work is if elements of the military defect and a civil war breaks out, with the rebels receiving international support. The degrees to which would vary depending on the nuclear threat, which…given that their opponent is fascist and thus not very sane, the support would be subtle.
But ignoring all that, let’s just assume it’s a vanilla tyranny. If the people and not the military rise up, they will be labeled as terrorists. These terrorists won’t have to worry about the military though, because the FBI and all the other alphabet agencies in this country will be systematically hunting them down. The FBI has tabs on all of these insane far right militias in case they try anything, and if they’re crazy enough to try it the FBI swoops in to arrest them all before they even have a chance to carry out their plan