Sociological studies suggest that increasing contact between groups can yield familiarity and tolerance. But it can also unnerve, especially in communities where that rapid change is most visible — and when politicians stand to gain by exploiting it. California lashed out at diversity before embracing it.

“There’s a very rich history of xenophobia, of racism, of trying to wipe each other out,” said Connie Rice, a longtime civil rights lawyer in California. “It’s not like we were all of a sudden born the Golden State.” State leaders pushed for the internment of Japanese Americans during World War II. “This is where the Chinese weren’t even allowed to own property,” she noted….

Rush Limbaugh started building his following as a right-wing radio talk show host in Sacramento in the 1980s. The ’90s in California brought the Rodney King riots, a strict three-strikes law, the contentious Proposition 187 fight and ballot measures in which voters rejected affirmative actionand bilingual education. “We went through a pretty chaotic last 20 years,” said Manuel Pastor, a University of Southern California sociologist.

But this is the same state that today vows to defend immigrants from deportation, a place where voters have supported a higher minimum wage and prison reforms that benefit minority residents. “You would not have predicted that from amid that chaos,” he said.

The demographic change California underwent between 1980 and 2000, Mr. Pastor said, mirrors the change (and projected change) in the United States since 2000 and up to 2050, when whites are expected to be less than half of the nation’s population.

“The United States just went through its Prop. 187 moment,” Mr. Pastor said of this presidential election. The question is whether the rest of the country can adjust faster to demographic change — or with less conflict — than California did. “Why go through all of our pain? That was no fun, and it dashed a lot of people’s lives. We underinvested in education. We over-imprisoned, so we got a lot of people locked out of the labor market. We broke apart a lot of families because of anti-immigrant sentiments. We did a lot of stupid things to ourselves.”