I think he could have beat Nixon.
It's hard to say because Jack really wasn't that popular in parts of the country, and Bobby was looked at as Jack's pit bull.
I think in RFK v. Nixon.... the only State Kennedy loses that Humphrey carried would have been Texas. All of the rest of the States where JFK wasn't popular were either solidly for Nixon or solidly for Wallace.
Here's the Actual Electoral College Vote:
Nixon: 301
Humphrey: 191
Wallace: 46
So if Kennedy loses Texas (25), that brings him down to 166. On the plus side, though, he was a better campaigner than Humphrey, so he should have picked up some marginal states from Nixon... Let's say the following States swing to Kennedy:
Missouri (12) (Nixon carry by 1.13%)
New Jersey (17) (Nixon carry by 2.13%)
Ohio (26) (Nixon carry by 2.28%)
Alaska (3) (Nixon carry by 2.64%)
Illinois (26) (Nixon carry by 2.92%)
So that leaves the race looking like this:
Nixon: 242
Kennedy: 250
Wallace: 46
Now the key question is this... was Kennedy a good enough campaigner to swing California (40) (Nixon carry by 3.08%) over to his column? True, Kennedy did win the California primary... but only just barely, and that was against Eugene McCarthy. California was Nixon's home state... and it had a popular Republican Governor in Ronald Reagan. If Kennedy wins it, he wins the Presidency outright. But I'm thinking winning it would have been an uphill struggle.
So if Nixon carries California, then the Election goes to the House of Representatives. The Democrats have a majority there... but now George Wallace is in the catbird's seat. So how do the Southern Democrats in the states Wallace carried vote? Do they go for Nixon or Kennedy? I'm thinking they go for Nixon... the only question is how much of his soul would he have had to sell to Wallace?
Would have been a pretty dramatic ending to an already dramatic year, I think.