What if, as expected, Barry Goldwater lost the 1964 California primary to Nelson Rockefeller? Rockefeller had mounted a strong advertising campaign in the state and Goldwater's extremist positions seemed to put him behind. The primary was a big delegate haul and was seen both at the time and afterwards as pivotal to the chances of a Goldwater victory on the first ballot at the 1964 Republican convention. The standard AH.com PoD of Happy Rockefeller not having a baby before the California primary would probably be enough to allow Rockefeller to get a narrow win as it reminded voters of Rockefeller's personal life and remarriage.
What would be the effects of a Rockefeller win? Contrary to some alternate histories I've seen, this would probably not result in Nelson Rockefeller being the 1964 Republican nominee. Rockefeller simply did not have the delegates or support to win the nomination, though his victory in California could have kept Goldwater from winning the nomination outright. Even Rockefeller acknowledged that, he released a widely published brochure that showed Goldwater standing alone outside while Rockefeller was pictured with Richard Nixon, George Romney, Henry Cabot Lodge and William Scranton. Before the Storm says "the purpose of the pamphlet was to hint that Rockefeller would not necessarily be the leader who stopped Goldwater-that by voting for Rockefeller's delegation, you were actually voting for whichever person the moderates anointed at the convention to stop Goldwater from his first-ballot victory."
Of those moderate candidates, I would consider Governor Scranton of Pennsylvania to be the most likely candidate-he had the least baggage and was a popular Midwestern moderate, and he was the OTL choice as the leader of a last minute stop Goldwater effort. Scranton would have a far greater chance if Goldwater did not win California and get 86 delegates from the primary. However, Goldwater's superior delegate organization and dominance in the South and West would still put him close to victory, though it is possible he would fall short at the first-ballot, and hundreds of Goldwater's delegates were determined to vote for him no matter what, come hell and high water, with such messages of support as "WILL VOTE FOR YOU IF MY VOTE IS THE ONLY VOTE YOU OBTAIN" and "I AM PREPARED TO STAND BY YOU AS RESOLUTELY AS DID GENERAL THOMAS FOR THE UNION AT CHICAMAUGA."
So, 1964 goes to a brokered convention, and while Goldwater does come first, he falls short of a majority. Scranton is the moderate candidate and ultimately wins the nomination. According to polling by the LBJ campaign, Scranton was the strongest Republican candidate. Even Scranton though would likely lose in 1964, given how LBJ had peace and prosperity, was popular and had Kennedy's martyrdom.
How would 1964 go down-ballot? What would be the results? What would be the effects of no Goldwater nomination? Longer term, how would the 1968 election be affected? Would Ronald Reagan still be a major political figure without his famous 'A Time For Choosing' speech? How would the conservative movement be impacted-would they still end up dominating the Republican Party? Would the realignment which resulted in states like New England states like New Jersey and Vermont being solidly Democratic states and the South turning to the Republicans still occur? What if?