I fear.

I think they are betting trump will lose. Sabotaging the vax program keeps COVID-19 in play in the economy, thwarting Biden's recovery plan.

Or am I giving them too much credit for thinking realistically and this far ahead?

disseminating dangerous misinformation about vaccinations

He is an outlier, just like those on the right on this subject

Liberal, conservative, Green, Libertarian, all of them use the same lies and smears.

It is a shame...He was not a bad guy in other ways (I am thinking circa 2004 etc.) . He was an environmental lawyer if I recall right and a generally ok sort of guy.

However, he seems to have really gone around the bend:
https://www.thedailybeast.com/trumps-ex-wife-marla-maples-and-robert-f-kennedy-jr-push-wild-bill-gates-coronavirus-conspiracy

Wonder what happened to him. He is an educated man and not a right wing nut. How did he get this nutty?

A few, (fortunately only a few,) actually develop a form of mental illness.
Paranoid schizophrenia is one.

Others have a particular experience, and that convinces the person they are correct, no matter how crazy the belief.
I knew a guy in a job I had decades ago, who was convinced Santa Claus was real.
Complete with flying sled, North Pole home, etc.
He had "Seen Santa in his sled on his roof!"
I asked the guy was it possible it was just a very vivid dream he had? (I've had some even weirder)
Nope, he was set in his belief.
Otherwise, he was normal.

Others read an article, or see a video on the Internet, and are "recruited" that way.

As to Kennedy?
I think it's the third one.