If recent population trends continue at their current pace, it’s likely that by Election Day this November, minorities will constitute the majority of the population in the Congressional District centered on this prospering small city in Orange County about an hour south of Los Angeles.

That places the 45th Congressional District of California, whose seat is now held by Republican Rep. Mimi Walters, at the forefront of a trend that’s steadily reshaping the landscape of House seats across the country: the inexorable growth of racial and ethnic diversity.

A CNN analysis of census data found that from 2010 through 2016, the latest year for which figures are available, the minority share of the population increased in all but 24 of the 435 congressional districts. In 123 districts, the minority population increased over that period by at least 3 percentage points, or half a percentage point annually.

The result was that the number of districts where minorities represent at least 40 percent of the population increased by 22 just from 2010 through 2016, reaching 171 in all. That’s nearly 2 of every 5 districts and that number is certain to crest even higher by the next census in 2020.

“That’s the demographic tide that is rising,” says Douglas Massey, a Princeton University sociologist who studies population patterns.

Orange County exemplifies as clearly as any place in the country both the opportunities created for Democrats by increasing diversity and the obstacles that might still frustrate them. Now the sixth largest county in America, with over 3 million residents, it sprawls from breezy beachfront mansions in Newport Beach and Laguna Niguel to gritty working-class neighborhoods in Santa Ana and Fullerton.