People forget how long the suburban-growth trend towards Republicans lasted in California; relative to the nation, the state's Republicanness peaked sometime around Reagan's first election. Because of how fast it became a Democratic-leaning state after this (it was zooming left in the 1980s, and already a sine qua non for Dukakis), the fact that it was barely if at all right-leaning in the 1940s and 1950s has kind of been forgotten. (It was certainly to the right in the 1964-1980 set of elections, though; 1972 merely showed that left-wing candidates there had a high floor).
It seems as if in almost every election from 1948 through 1992, the nationwide winner did worse in California than his national average. The only exceptions to this were in 1952 (Eisenhower), 1968 (Nixon), and 1980 (Reagan). Stevenson (in 1956), Goldwater, McGovern, and Mondale all did better in California than their national average. Hence, it suggests that there was a relatively high floor for both parties in California during that era. Eisenhower "only" won California by 11% in 1956 and Nixon by 13% in 1972, much less than their 15% and 23% margins of victory nationwide.
