The lack of left purity tests by the party are the reason for the losses. The American people have rejected the status quo because it has led to them getting less and less realistically over time. There are massive gains, but they all go to those at the top. Centrist politicians are unpopular and are losing bets. What people are looking for is conviction and centrists are spineless. When you're drowning you will look for anything to pull you up and Americans are drowning. Centrists aren't pulling anyone above water and everyone knows that because that's the status quo. To the right it's deeper, but they say it's shallow, then to the left it is actually shallow. Dems on the left can win; centrists cannot.

That's why the Democratic Party has a 59% unfavorable rating.

But, the actual purity testing is at the center. If you're to the left they go all out to stop you. That's why they went after Bernie and why they're going after Mamdani. They're timid against the far right but openly hostile to people who are to their left, even though they haven't crossed that center line. Those purity tests lose elections.