That’s an immediate hurdle for the GOP, which has long counted on suburban strength to offset Democratic votes in the cities. It could be an even bigger problem in the longer term because those suburbs are among the nation’s most economically dynamic, growing regions.

The shift reflects changing demographics: As with Orange County, many of the nation’s suburbs have become racially and ethnically diverse, shedding their status as all-white enclaves.

It has been accelerated by Trump’s weakness among college-educated, white voters. That group has sided with the Republican in every presidential election since reliable polling began in the U.S. in the 1940s, but this year it has consistently shown a Democratic majority in polls.

Because of the demographic changes, “the question is not whether or not a Democrat is going to win in Orange County, it’s just a question of when,” said Jon Fleischman, an influential conservative blogger who lives in Anaheim Hills.