This is another one of Trump's half-assed moves since he was shot.
Firstly, he appoints Vance as his VP, which did not go over well with much of his fan base, who wanted Vivek, or one of his long term trusted allies like Carson, but some wanted RFK jr.
So, he goes ahead and appoints Vance, and it falls flat, then when Trump gets RFK's endorsement he brings him out on stage and acts as if he is the VP. The crowd all cheered him, and RFK did some campaigning on the stage. The buzz was good for about a week after that, until it became evident that RFK probably won't even have a position within the admin. Now it's just lame, yes RFK is on board, but for what, if anything by the time Trump wins? Wouldn't be the first time that Trump has kicked someone to the curb after leading them on with promises of grandeur when he takes power, ask Steve Bannon and Chris Christie.
Regardless of some of RFKs political views, how powerful and symbolic would a Trump-Kennedy ticket have been?