The Left starts winning, but the people in left-controlled districts begin feeling an uncomfortable "this isn't what I voted for" sense of dread. This leads to internal strife, as traditional Democrats fight to take back control of the part, while the Right watches. The Left's winning streak begins to wane, and the Right entrenches itself for the next decade.
-PJ
I think that is what is already happening and what will lead to scenario 1. :)