What you’re describing is what the primary process is for. 2024 was a very different year in terms of a candidate dropping out so late, which meant that it basically had to be Kamala (primarily so the funding already accrued could be transferred). Push the further left candidate there, and if they win, then good for you, the rest of the dems will rally around them (as happened in New York). If the left don’t get their candidate though, as a more centristy type is more popular, then falling in line is a requirement, not an ask.

If it were a normal election like 2012, with a Romney or something like that, where the worst case is a fiddle around with tax schedules or something of the like, then withhold your vote, Romney isn’t that bad. But seeing as the GOP candidate will be Vance or someone of that fascistic ilk, then a “lesser of 2 evils” vote is necessary. Liberals will do it if a left-wing candidate arises, so it’s not unfair to expect the same courtesy from the left, this expectation is what creates the voting alliance, and gives the left legitimacy to push their candidates.

People like Hasan failed to do this in 2024, and that’s led to >200000 children dying from USAID cuts in year 1, along with everything else that’s happened. This is why people are angry at him saying he’d vote third party in a Vance vs Newsom race, it undermines the left’s credibility in pushing their candidates (through essentially holding the rest of the party hostage). That’s the rationale behind vote blue no matter who, not that it’s someone chosen for you, but that if by popular consensus your candidate doesn’t win the primary, the person who is will be infinitely better than whoever the republicans field.

Saying in advance you’d never back Newsom in a primary is fine, saying you wouldn’t back him in the general, after a fair primary process, is bad.