Democrats did everything they could to shun Kennedy, including refusing to hold debates between him and Biden and failing to provide Secret Service protection, even after Kennedy faced a serious threat of violence. If his independent campaign winds up taking support away from Biden, it will serve Democrats right for their poor treatment of him.
RFK Jr. should have expected that his public criticism of the Democratic National Committee would earn him little help in mounting an unprecedented challenge to an incumbent president. His dangerous conspiracy theories and his embrace of some far-right political figures probably make him a better fit for the Republican Party, or as someone who will actually take support from Trump and the GOP.
RFK Jr.'s entrance as an independent candidate will no doubt hold an anti-establishment appeal, but the question is what the impact will be. He may very well take votes away from Biden, yet Trump is also preparing to mount an offense in case the reverse is true. Likewise, Kennedy's run may fizzle after the novelty wears off. Or this may grow into something major that no one — not even Trump, Biden, or Kennedy himself can wrap their head around right now.