was a unique year in our nation's history. A lot of good, and a lot more bad. By late '67, within the party, those in DC knew that LBJ was becoming increasingly unstable. Several insiders who knew his character believed that he would not run again. When some activists tried to convince RFK, and then McGovern, to challenge him in the primaries, neither would do so. McCarthy, of course, was willing to, and announced his candidacy at the end of the year.
Nixon would win the republican nod, but it wasn't clear in early 1968 that he would. They had a fairly strong group of candidates. One can only speculate if LBJ had run, if he would have won that year. Events at the convention suggest not. I've always found it odd that among the older RFK supporters, after his death, relatively few supported Humphrey. Had HHH distanced himself from LBJ on the war publicly even a week earlier than he did, the late polls indicate he'd have won. But too many older RFK supporters voted for Wallace as a protest. I suspect they had liked RFK's law-and-order phase that lasted through his serving as Attorney General, but that is just speculation on my part.
By '72, the Kennedy Democrats no longer enjoyed the #1 position in party politics. Teddy was damaged goods. As we know from his autobiography, Humphrey -- a truly decent man - could never get over his bitterness towards JFK and RFK. I think Muskie was the strongest of our candidates over all. But the "rat-fuckers" had agents in the Muskie, Humphrey, and McGovern campaigns. They had access to campaign plans, letterhead, and unlimited money. And they were "good" (capable) at doing what they did to create great tensions and hostilities between the three camps.
In my opinion, other than Carter's win in 1976 despite the lack of real party unity, it wasn't until 1992 that Bill Clinton was really able to put things together. He did again in '96, and it wasn't until Obama's powerful coalition that our party accessed its real potential for power at the national level.