Robert Kennedy would not have won the Democratic nomination for President in 1968. The thought that RFK would have won had he lived is just romantic hindsight. I include a video from ABC TV analyzing his chances on the very day he won the California primary. Hubert Humphrey already had a majority or near majority of the delegates pledged to him. The Video is Here:
https://www.youtube.com/watch?v=oMr97_M7okwRFK even states in the interview that without Eugene McCarthy's support, unifying the anti-war candidates for President, he would not be able to win the nomination. McCarthy and, for the most part, McCarthy's supporters, hated Kennedy.
Here is "On To Chicago" a terrific book on this very subject; if RFK had lived:
https://www.amazon.com/Chicago-Rediscovering-Robert-Kennedy-Campaign/dp/1944229981Should somehow, RFK had won the Democratic nomination, he would be leading a badly fractured party, with a sitting President of his own party in opposition, and with George Wallace taking formerly Democratic votes in the South and industrial Midwest and North. He would have lost the election much more handedly than Humphrey did.
America was a much more conservative nation in 1968 and the voting age was 21, not 18. Nixon was the perfect candidate for that year. A nostalgic figure who promised to restore law and order to a chaotic, violent time in America's history.