The biggest reason Democrats keep getting worse is their competition, not the fact we vote for them in spite of deep flaws. Every time the Republicans win, Democrats insist they need to court centrists and move right. Every single time America proves they’re willing to elect someone even worse, Democrats take that as a sign to degrade further.

Republicans pull the US political spectrum to the right while Democrats act as a one-way ratchet preventing us from sliding back to the left. Like any ratchet, though, they’re not an effective tool for maintaining heavy tension/torque/whatever long term. The process only works when Republicans consistently come alone and pull to relieve the pressure. If that stops happening, Democrats start failing at their jobs like a ratchet put under too much strain and breaking. And that would be trivial if more people voted. Republicans are highly dependent on gerrymandering and voter suppression to maintain power, so if leftists overcame their electoral defeatism and actually voted for someone who has a strong chance of winning, we could start making that a reality.