Nader, or Jill Stein or any third party candidate that runs in the general is going to syphon votes from a Democrat or a Republican. This is part of why the biggest fear of Republicans is Trump breaks off to run as a third party candidate...if he does, he would be a huge third party candidate that would, like all third party candidates, lose the election but he would wipe out the Republican candidate and lock in a win for Democrats. 

Bobby Kennedy is not going to run in the general. He will be running in the primaries against Biden. Biden will treat him like he does not exist. The entire Democrat party will act as if he is invisible. He would never get on a debate stage with Joe. Biden is locked in as the Democrat unless he suffers a health issue. The media, mainstream legacy media, will basically black him out and talk about him as if he is a nut. If he gets mentioned, it will only be to run him, his past, his very existence down, and to throw in some lies about him. 

The mainstream media is all in on the main event being Biden vs Trump. Biden, as long as his health is good, will destroy Trump. You will only find mention of RFK Jr. on the internet. He may get 20% of the vote in primary voting. Maybe a bit more if he gets enough attention, but that means he will lose big to Biden and the media will label his campaign pathetic. 

Now, do I think RFK Jr. is a stronger candidate than Biden? I do. Do I think he would destroy Trump or any of the other Republicans in a general election? Oh yeah, I do. He has some very interesting things that work for him BUT his massive disadvantage is that the party he is running for, under their banner, does not want him. So, that will be that. 

What I dislike is that the media and the Democrats will just run him down and talk shit about him, and just plain old make up lies about him. That's the game. Interesting that he is running, I like the guy, he's not going to be president and won't be in a position to harm Biden.