It was close, sure, but Nixon's running mate (Henry Cabot Lodge) wasn't worth much at all on the campaign trail. He was selected as a possible counterweight to Democrat inroads in New England, and wound up with his liabilities (a nap every afternoon, no matter what) balancing his assets. Even as a kid (I was eight in 1960) I remember a lot of people saying that if anything happened to Nixon, Lodge would be another Coolidge. No idea what that meant at the time; I learned later they figured he'd be a low-energy, not-doing-much president. Thus it came as no surprise that Lodge wasn't on the ticket in '64. Accounts vary but most say it was mutual: Nixon was less than thrilled with Lodge and Lodge was bored. Nixon's choice in '64 of Theodore McKeldin of MD was a strong move: he actually pushed MD into the GOP column for a while (no mean feat) and shored up the GOP in the rest of the middle Atlantic states. I always thought it was a shame he didn't get the nomination instead of Rockefeller in 1968.
For what it might be worth, though, there wasn't a huge amount of difference between Rockefeller and Scoop Jackson in 1968. They had similar approaches to the cold war, civil rights, and the space program for starters. Maybe that's why turnout in the south in particular was so low that year: more than one commentator said the election pretty much came down to a coin flip.