Being willing to throw an election is one of the only tools voters actually have to fight fascism. It's the only way to prevent a bait-and-switch candidate. If you're not willing to potentially lose an election when your candidate betrays you, future candidates will betray you every time. You've told them that you're perfectly fine with being betrayed. You've proven yourself a spineless cuck that will let people walk all over you.
Actions have consequences. Voting has consequences. And Trump isn't the worst possible leader out there. He's a monster, but there are many gradations of monster. There are far worse monsters out there waiting to be elected. If you're not ever willing to walk away from a traitor candidate in the general election, you guarantee that the Democrats will just keep sliding to the right forever. Nominating a corporate Dem in 2028 will almost certainly see another Republican win. But even on the thin chance they do win, electing a corporate Dem in 2028 guarantees someone even worse than Trump winning in 2032.
We've degenerated so far precisely because Democrats don't take responsibility for their votes and will just blindly vote for whatever corporate tool is placed in front of them. It's the political version of the "next quarter" thinking that plagues corporate America. All that matters is the election today. Don't think about the long term consequences. Focus only on today, even if it hurts you in the long term. Trump is the result of decades of Dems kicking the can down the road, holding their nose, and voting for the lesser evil.
Notice, we're only starting to see some progressives gain traction in the party after Democrats have suffered badly at the polls. There has been real change at the DNC. That and candidates like Mamdani would have been completely impossible if Trump hadn't been elected. It's only when the old guard loses horribly and has to run away in shame that the opportunity arises for new voices to take the reins of the party.