There were only a handful or primaries contested back then and California's wasn't coming until June.
Then U.S. Senator George Murphy was a former actor who surprised many in 1964 by bucking Barry Goldwater's loss in California and beating Democrat and former JFK Press Secretary Pierre Salinger.
I suspect Murphy's example helped to inspire the GOP to put Ronald Reagan up at its candidate for Governor or California in 1966.
Reagan was in or out of the race depending on what you wanted to believe.
First in line after the Goldwater loss in 1964 was Richard Nixon, with Nelson Rockefeller entertaining hopes of coming back in 68.
Rockefeller's 1964 effort was crushed after he divorced his first wife and married a younger woman.
It turned off women voters especially.
I fear we Republicans are in the same position politically that the Democrats were in the 1968. Weak candidates and scrambled messages. The other side wins mostly by default.