Lets say New York Governor Nelson Rockefeller manages to secure the Republican nomination (perhaps Scranton and/or Romney throw their support behind Rocky to unite against Goldwater), how does the 1964 election go?
First of all, this is very unlikely (even without the divorce and remarriage) for reasons I go into at
https://www.alternatehistory.com/forum/threads/wi-rockefeller-64.494995/#post-20951243 As I also state there:
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If Rockefeller were somehow nominated, I have little doubt LBJ would defeat him handily. Of course Rocky would get the votes of many moderate or liberal Republicans who voted for LBJ in OTL. But Wallace would run and get most of Goldwater's OTL vote in the South and even a substantial vote among embittered conservatives in the North and West. Indeed, even apart from a Wallace candidacy, the polls did not show Rockefeller that much stronger a general election candidate than Goldwater:
"Mr. Harris reported that among voters generally President Johnson was favored for re‐election by 52 per cent, while 33 per cent would vote for Mr. Lodge, leaving 15 per cent undecided.
"The next‐best showing in the Harris poll was made by Mr. Nixon. It was indicated that he would attract 32 per cent of the total vote in a race against President Johnson, who would be favored by 61 per cent in such a contest.
"The Harris poll of all voters also showed that President Johnson would defeat Governor Scranton by 61 to 28 per cent, Senator Goldwater by 66 to 26 per cent, and Governor Rockefeller by 69 to 23 per cent."
https://www.nytimes.com/1964/04/07/archives/poll-calls-lodge-gops-top-hope.html
One thing to remember is that 1964 was a year of prosperity and peace (people did not think of Vietnam as a full-scale war yet) and that under such circumstances most people did not want the US to have a third president within 15 months. (And some of those who
were passionate about voting against LBJ hated him because of civil rights and would have opposed Rocky's stand on that issue ar least as much.) Add to that the fact that no matter who wins the GOP nomination, the GOP will be a very divided party, and it is hard to see the GOP winning or even coming close.