It's kind of a don't-care for me:
* RFK Jr. had zero chances of becoming POTUS, and other than POing Dems, causing some to lash out, not much influence over anything;
* How RFK Jr. might influence voting was a matter of speculation; some thought he would attract single-issue-voting anti-Covid-vaxxers, some thought he would attract disaffected Dem voters; my opinion, which with a fiver will get you coffee and change at 7-Eleven is that RFK would have affected Biden worse than Trump (Do you want cream or sugar with that?);
* I think RFK Jr.'s endorsement of Trump stems from how the Dem Party crapped on him and Biden refused him Secret Service protection.
Trump is good at making appreciative noises, but only time will tell whether RFK Jr. will get more than that.