You can’t out-crazy Donald Trump. You know it, I know it, and he knows it. Since RFK is increasingly sounding like a Trumpian conspiracy theorist, Trump won’t have to pay him any mind. He’s not going to lose any portion of his base, let alone votes from Nikki Haley supporters, to a second-rate version of himself.
Biden is in a different position; he could lose votes to ignorant progressives who assume that RFK is one of them simply by virtue of his name. He should be running commercials on the web reminding the blue base that RFK is an anti-vaxxer who supports the January 6 rioters and Israel’s actions in Gaza. That should do the trick.
In the long run, I think Biden will have a greater problem with young progressives voting for West or Stein. They represent a more ideologically coherent threat to him than RFK does.