If RFK ran as a third party he'd take votes from the Republican candidate, not the Democrat one. What kind of Democrat is going to vote for someone who believes vaccines cause autism and HIV doesn't cause AIDS?
Before COVID, I would have guessed the biggest reservoir of anti-vax sentiment was among very liberal Democrats (think the people who are super into yoga, organic food, and naturopathic doctors).
COVID became a culture war issue, which lead to partisan Democrats lining up on the pro-mask, pro-lockdown, pro-vaccine side, but I have no idea if that disrupted the views of existing anti-vax Democrats (of the "vaccines cause autism" variety).
>RFK Jr. pulls more votes from Trump than Biden in three-way race: Poll
https://thehill.com/homenews/campaign/4289365-rfk-jr-trump-v...
RFK's promoters switched to promoting Phillips when they realized RFK was drawing more conservatives for the antivax stuff, than democrats for the Kennedy name.