Hillary Clinton's remark about Robert Kennedy's assassination in June after the California primary has been widely commented upon, and I don't want to attribute any dark motives to what she said, but it's worth looking at the comment in the context of what she says she meant, which is that it is not unusual for candidates to be competing in primaries in June.
She first referred to her husband's 1992 primary contests, and how he did not "wrap up" the Democratic nomination until he won the California primary. That is only half true. Bill Clinton swept the "Super Tuesday" primaries in March (not February) and was considered the nominee apparent after that. Paul Tsongas withdrew from the race later that month, leaving only one other candidate still campaigning, Jerry Brown.
California was one of the last primaries and Brown had won only three states, New Hampshire, Colorado, and Connecticut, so he had virtually no chance at the nomination. (Clinton won 39 states, including California, and Paul Tsongas won 6.) Brown apparently thought that, if he could win California (his home state, in which he had served as governor) by a large margin, he might be able to deny Clinton a first-ballot victory and perhaps play the role of spoiler.
In trying to justify her continued campaign by reference to the 1992 primaries, Hillary is comparing herself to Jerry Brown, the spoiler, and not Bill Clinton, the eventual nominee. And California was (and is) a big state, with lots of delegates at stake, and was Brown's home state, which he had a reasonable expectation of winning (although he did not). How does that justify Hillary Clinton continuing to campaign in Puerto Rico, Montana, and South Dakota?
The reference to Robert Kennedy campaigning in California in June of 1968 is even more of a reach. The eventual party nominee was Hubert Humphrey, who declared his candidacy only after President Johnson made the surprise announcement in March of 1968 that he would not seek reelection. Entering the race so late, Humphrey was not able to register for any of the primaries, and so he did not win any primaries at all. Becoming the nominee of the party without winning a single primary was possible then because the majority of Democratic delegates were what we would now call "superdelegates" chosen by political leaders and not by primaries or caucuses. It was only after the Democratic party changed its rules during the 1968 convention itself that the primary system began to have real political importance.
In the 1968 primary campaigns, Robert Kennedy (and Eugene McCarthy) were trying to do what John Kennedy had done in 1960, which was to use the primary system as a springboard to challenge the political establishment. But Hillary Clinton is the political establishment. She is now hoping to use the last few primary contests to challenge the candidate (Barack Obama) who has proven to be the more popular candidate, winning more total votes than she received in the contests in which they competed.
So where does that leave Hillary Clinton? It leaves here exactly where she is now, continuing to compete in a race she can't really win and looking for some justification other than her own personal ambitions.