The presence of Nelson Rockefeller as the Vice Presidential candidate on the Republican ticket pulls in Rockefeller's home state of New York, of which he was Governor at the time, and very well liked in the state, and pulls in the neighboring state of New Jersey, where the Rockefeller name is well known. In 1960, Nixon lost New Jersey by only 0.80%, and with Rockefeller on the ticket, this is enough to tip the state to Nixon.
Nixon wins the Presidency in 1960 instead of in 1968.
Nixon/Rockefeller 281
Kennedy/Johnson 237
Unpledged Electors 19