The far-right is the most militant and by far outnumbers the far left. Right now, if things were started anew, it would be a new far-right government. A militant far-left uprising would literally just get murdered, and most republican voters would be ok with it.
A course of action that seems obvious to me (I may be wrong) would be for left-wing people to organize within the Democratic party to get left-wing people elected as Democrats. Kinda like the “Tea Party” or MAGA movement.