The suburban moderates who voted Republican for President in the 80s fell in love with Bill Clinton and the Democratic Party in 1992 and never came back. California back in the 60s and 70s was a pretty conservative state as I understand, but Clinton changed all that.
I think the Democratic party owes Clinton a huge debt of gratitude for their resurgence at the presidential level over the last 20 years when compared to the 70s and 80s.
Even though Clinton was a southerner, suburbanites in California, the West Coast and NE loved him and remained loyal to the Democratic party even after he left office. When Clinton came into office, states like California, Illinois, Pennsylvania and especially New Jersey became strong D thanks to the increased support from their suburban voters.
And the above analysis is amazing! I learned a lot from it. To be honest, it looks like a lot of the shift can be explained simply from white voters moving out of California. The state went from 57% white in 1990 to 40% white in 2010. The census also projects that the state will become majority Hispanic next year.
So how can California go Republican when the white vote is decreasing while minorities like Hispanics and Asians vote in larger numbers and consistently vote Democrat?