Exactly what it says on the tin. John Kennedy is never assassinated. Without getting into a lot of arguments over what happens in 1964, presume Kennedy is a two term President. After Kennedy's years in the White House, the Democratic Party is tasked with selecting a successor. Now in my view, the two most discussed successors for President Kennedy in 1968 are not particularly plausible. I doubt LBJ would run. Johnson's decision not to seek the Presidency in 1968 was not merely the consequence of New Hampshire. He was afraid of his health failing during a 1969-1973 term, and he was generally terrified of dying in office. While the Presidency's extra stress doubtlessly took its toll, Johnson may have similar health concerns come 1968 ITTL. And I very much doubt Robert Kennedy is going to get the nomination when his brother's Presidency ends. So, if not Vice President Johnson or the President's brother, who might the standard bearer be? Hubert Humphrey?