As a former BernieBro, I can attest to this. Purely anecdotal, so idk if it means much, but Bernie in 2016 was similar to Trump, calling out the same/similar problems, except that he said the solution was more government rather than private industry. When Bernie cucked, it blackpilled a lot of my friends, and increased their hate for Hillary (to whom this was really their first introduction to her).
When Bernie was back in 2020, some were a little excited for him to be back (though they admitted worry that "the system" would screw him over again). But then they were listening to him and when he started with his IdPol, they were /pissed/. They had been feeling the effects of it in their workplace since 2016, and so to hear him spout that stuff (as well as his pro-immigration hurting their worker beliefs) made them drop him like a hot potato.
They went to Tulsi (even I personally think she's nuts), and when she got shafted they told me they're just checking out of the election.
I brought up the idea of voting Trump as an anti-establishment vote, but to them the idea of voting R is anathema, so they're just sitting out.
It also is important to not discount the dem primary people who were "anyone but hillary". In fact, this is personally where I think part of the momentum behind socdem stuff is coming from. Instead of seeing, wow hillary was so hated people are willing to vote for a guy who has socialist leanings, they saw, there are more people who want socialism so we must push it now now now!.
As a result, it's necessary to account for the votes who were anti-Hillary only and may not vote for Trump again. After all, they might be neo libs who hated Hillary for other reasons and would vote for a different neo lib.