Kennedy was never going to be the nominee. Lyndon Johnson would’ve moved heaven and earth to make sure he wasn’t the democrat nominee in 1968 Kennedy got a very late start and the only major primary one was California when he died.
Historians debate whether RFK would have been the nominee—but I was politically active even in 1968 (yeah I am old) and at that time I and most everyone I knew believed he was going to be the nominee and the next president.
We could have been mistaken but that was our view at the time.
His speeches were leftist of course but like JFK he was an outstanding public speaker,
Humphrey and Nixon were not even in his league.