"Motivated reasoning" involves rationalizing an existing belief rather than conducting or relying on objective research. There's no shortage of it when commentators weigh in on developments in the public policy arena.
All kinds of explanations and data points have been thrown about to explain Californians' tremendous change in attitudes over the last several decades. Many of the explanations I have heard appear chosen on the basis of what justifies the speakers' pre-existing beliefs.
I decided to take an objective look at the relative strength of political parties in California over the last 100 years in a search for answers.
To do it, I had to first determine what measure of strength would be the most meaningful. Relying on party registration trends would prohibit comparisons with other states that lack registration by party. Looking at statewide offices or Congressional districts would provide too small a sample.
I determined the best measure of a party's political strength in a state is the number of seats it holds in the state legislature. This measurement provides a large number of election results to look at, providing a clearer picture of what has occurred over time. The quirks of particular statewide races would provide wild variances in the data, while trends in legislative seats provides a larger sample size and a sound basis for comparison between states.
In the presentation you may download below, I conclude that several myths concerning the decline in Republican voting strength in California. One such myth asserts Republican decline began in 1994 as an alleged Latino-led blowback to Proposition 187, the measure supported by then-Gov. Pete Wilson to deny certain public benefits to illegal immigrants.
A review of the data shows the decline actually began decades earlier.
Meanwhile, as Republican strength has declined in California, a mirror trend can be seen in Missouri.