I hate to rain on the Kennedy parade, but I think Robert Kennedy would have been a poor president.
The record shows that by the late 1960s, Kennedy was strongly wedded to liberal ideas about the role of government that have proven in the years since to have been a miserable failure.
All the charisma in the world can't change that. I agree that RFK was somewhat better than some of the other liberals who followed him, but that's not saying much.
I think you underestimate how a Robert Kennedy Administration could have dealt with the trials of the late 1970’s or early 1980’s. Unlike Teddy and like Jack he was a pragmatist and interested far more in what worked and what was practical than what might seem ideologically pure, sure he was in values very much like LBJ or Teddy but in his implementation of these I think you would have seen polices not dissimilar to the leftwing in Australia “monetarism with a human face” spending cuts and more progressive, yet far reaching tax cuts and a hawkish foreign policy.
You may be right, but we'll never know. If Kennedy had lived and been elected in 1968, he would have left office in 1977 at the latest, so he wouldn't have been dealing in any case with the issues of the late 1970s and early 1980s. He would surely have taken a different turn in Vietnam than Nixon, but no doubt with the same end result. Maybe we would have avoided some of the partisan bitterness that grew out of Vietnam, but maybe his Vietnam policy, without engaging the Russians and Chinese as Nixon did, would have produced a disaster.
I agree with you to a point - he would not have been the dreadful doctrinaire liberal that his brother became. But maybe he would have evolved in that direction. There's no way of knowing. That is the one benefit of dying young - nobody sees you age, and people can assume the best about how you would have aged and developed.