"My initial reasoning as to why the Democrats are terrified of RFK jr. (because they fear he's turning moderate Democrats & Independents into Trump voters) is still very plausible, but after rethinking it I come to another conclusion.
Democrats won't allow Biden to be the nominee, especially after the FBI 1023 news came out today. He's done. But when they get rid of him it will create an open primary. Democrats don't want this. They want their candidate to be anointed, not selected by voters. This is why the DNC announced they won't hold any debates. They don't want someone like RFK jr. debating someone like Newsom. It would expose how radical the party has become.
Also, the reason that the DOJ is using lawfare to attack Trump is because they want the entire election cycle next year to be focused on Trump's legal problems, not their record of destroying the country over the last 4 years. Having an open primary and debates will prevent the focus from being solely on Trump.
Their plan is to get rid of Biden, rig the primary for Newsom, and keep the focus on Trump all of next year. For that to happen they can't have RFK jr spoiling it by rising in the polls, which would result in voters demanding debates. Hard for them to keep that from happening if RFK jr. is remotely close to Newsom in the polls. Therefore, they must destroy him before his poll numbers warrant debates.
If his poll numbers rise to a level that warrants debates, and the DNC denies him that opportunity, his voters will be livid and vote for Trump in the general out of spite, which leads back to my original hypothesis."