I think it's important to highlight the importance of primary elections here. Unlike most other countries, the process of choosing who a party nominates to stand for election is entirely controlled by voters in the USA through primary elections.
The Democratic Party loses because the Republican Party nominates populists that people are excited to vote for. If the Democrats want to win, they need to do the same—nominate people that voters are actually enthusiastic about.
Primary elections have historically rubbish turnout. If progressives, social democrats, and socialists want their candidates to be nominated, they should be starting information campaigns to get their fellow left-wing Democrats to vote in primary elections.
the process of choosing who a party nominates to stand for election is entirely controlled by voters in the USA through primary elections.
Courts have ruled consistantly that the political parties, which are private institutions, have control over all aspects of the primary process. Political parties are private tyrannies that put their agenda above the will of voters.
Of course that's true, but the rules surrounding superdelegates and other tomfoolery wasn't enough to make a difference in any recent presidential primary. 2024 was an anomaly but it seemed pretty likely Kamala would have won the nomination regardless (this is not an excuse to not hold a primary).
The rules for primaries to legislative or local offices are actually completely clean and fair, at least as far as I can tell.
The way we run our primaries is an absolute joke. The presidential race is over months before half the country has even had a chance to vote. That gives the establishment every opportunity to manipulate media coverage to boost their preferred candidate.
The way every single establishment candidate dropped out and endorsed Biden (who was near last place) on the same day was ridiculously transparent. I'll also go to my grave with absolute certainty that Warren stayed in because the establishment got to her. I don't know if it was a carrot, a stick, or both, but they kept her in the race as a spoiler. Warren completely dropped her campaign but refused to drop out for almost another month.
We should be up in arms about the Democratic primary process, not calling them "clean and fair". Everyone should vote on the same day, we should have ranked choice style voting, and debates shouldn't all be run by corporate media. That's the minimum we should accept.
As for the superdelegates, they are the perfect demonstration of how our of touch and clueless the party establishment is. It doesn't even occur to them that if they ever were to override the will of their voters that it would sink the party for a generation or more. There is no world in which they could do that then win the general.
The important part of a primary isn't the actual person, it's that they force the democrats to acknowledge what their base wants and pretend to want it too.
It's also the best opportunity candidates get to frame issues and demonstrate vision. Conventional wisdom is that a contested primary is bad for the general, but that hasn't been true for decades. Election after election, a contested primary wins the general.