As California’s final votes are counted, here’s how the midterms helped Democrats sweep Orange County

Orange County has long been a Republican stronghold. But this year, Democratic turnout propelled the state to the left, and the county went with it. Democrats won every congressional seat in the county, taking four seats from Republicans. With every vote counted in every precinct, here’s a detailed look at how, after years of Republican electoral strength, Orange County turned blue.

Let's go back to 2014. Orange County was reliably red, except for longtime Democratic strongholds in Santa Ana, Anaheim and Garden Grove.

After the 2014 midterm election, Orange County was politically polarized. Democrats and Republicans won their seats by large margins — none of the races were close.

In the 2016 election, the blue began to trickle from Garden Grove and Santa Ana into neighboring cities (most noticeably Irvine and around Laguna Beach), but it wasn't enough to flip any seats. Hillary Clinton, however, won the county, the first Democratic presidential candidate to do so in 80 years.

Note: Two Democrats ran against each other in the 46th district. There was no Republican in the race.

But after the 2018 midterm elections, those trickles of blue became a wave. Democrats held Districts 46 and 47 while winning every other congressional other seat in the county.

Changing demographics and higher-than-usual voter turnout contributed to Democrats' victories. Registered Republicans are on the decline in Orange County. Every city in the county has shed voters who register as Republicans, while Democrats have added to their ranks.

Source: Political Data, Inc.

In District 48, Democrat Harley Rouda defeated 15-term congressman Dana Rohrabacher by seven points. Rouda was aided by a shrinking pool of registered Republicans in the coastal district.

Change in registered Republicans between 2002 and 2018:

Huntington Beach: -9%

Laguna Beach: -10%

Newport Beach: -13%

In District 45, incumbent Republican Mimi Walters faced some of the largest drops in registered Republicans in the county. Democrat Katie Porter won almost every precinct in Irvine, one of most populous cities in the county, and ultimately won the district by four points.

Change in registered Republicans between 2002 and 2018:

Irvine: -20%

Lake Forest: -14%

Mission Viejo: -13%

Tustin: -19%

In 2016 Republican Darrell Issa held onto District 49, which includes portions of San Diego and Orange counties, by about 1,000 votes. His support was greatest in Orange County, where he won that part of the district by 20%. Issa retired, and Republican Diane Harkey held onto the O.C. portion of the district but at a lower 6.8%. That lowered support in O.C. helped propel Democrat Mike Levin to winning the district this year.

Change in registered Republicans between 2002 and 2018:

Dana Point: -10%

San Clemente: -10%

In District 39, Democrat Gil Cisneros did not win the majority of votes from Orange County or San Bernardino County. However, he won in Los Angeles County while capturing crucial precincts in Fullerton, Brea and even Yorba Linda, which once had the largest number of Republicans per capita in the state.

Change in registered Republicans between 2002 and 2018:

Brea: -13%

Fullerton: -16%

Yorba Linda: -9%

Sources: Orange County Registrar of Voters, Statewide Database at U.C. Berkeley Law, Political Data, Inc.