Bobby Kennedy, in all honesty, scared the Middle Class of America. He had a fanatical following from racial minorities and the poor, something Nixon could have exploited against him. We must remember, this is Richard Nixon who Bobby Kennedy is opposing, not Kenneth Keating.
Kennedy would have to smash the Democratic establishment in half to win the nomination, and thus we have McGovern four years earlier. Many Democrats in the Humphrey-Jackson-Muskie mode might “hold their nose” and vote for Nixon, like many blue collar Democrats did in 1972. Kennedy also would have selected a fellow progressive, most likely Iowa Governor Harold Hughes
Also, George Wallace’s vote totals would have increased amongst blue collar Democrats. Bobby Kennedy would have had the “New Left” and ethnic minorities, and Nixon would have had nominal Republican voters.
Nixon/Agnew (R): 274 EV
Kennedy/Hughes (D): 211 EV
Wallace/LeMay (AI): 45
In the end the map changes little, but RFK is defeated. 1968 was not going to be a Democratic year no matter who was nominated, too many forces were working against the Democrats.