San Diego County has become continuously more Democratic over the years, according to a review of registration data, with more than a dozen Republican-dominated ZIP codes switching to Democratic-majority since 2018.
More than 1.9 million people are registered to vote countywide, up nearly 2 percent from this same time two years ago, the registrar of voters reports.
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Of that total, nearly 42 percent, some 794,000 people, are registered as Democrats. About 27 percent are Republican, and one in four voters identify with no political party.
Today’s voter pool stands in sharp contrast to the population in 2010, when Republicans and Democrats in San Diego County were nearly equal in number, each party representing about 36 percent of the 1.4 million voters.
In 2004, former Republican President George W. Bush won 52.5 percent of the vote in San Diego County. President Joe Biden received 60 percent in 2020 — 23 percentage points higher than former President Donald Trump.
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“San Diego County as a whole has been trending Democratically for about two decades now,” said Seth Hill, a professor of political science at the University of California San Diego. “From 2008 forward, Democratic presidential candidates have won here, and that corresponds pretty directly with voter registration.”
Voter data show Republicans’ share of the voter population had dropped to 28 percent by 2018, with no party preference voters picking up more ground than in previous years. By this year’s midterms, independents’ share of the electorate had shrunk, and Democrats picked up most of the gains.
Jack Pitney, a politics professor at Claremont McKenna College, said this likely reflects what’s known as “the diploma divide” seen in politics nationwide, not just in California. San Diego County’s shift, he said, is most likely due to its residents’ rising levels of education.
Studies, exit polls and surveys show people with graduate degrees or some form of higher education tend to lean Democratic, and the share of San Diego County’s adult population with graduate or professional degrees has steadily climbed in recent years, data from the U.S. Census Bureau’s American Community Survey show.
“Educated professionals tend to move to the Democratic party — doctors, lawyers, people with [master of business administration degrees],” Pitney said. “We’re seeing the long-term effects of higher education and more access to education overall.”
How registration has changed over time
Areas of Carlsbad, Carmel Valley, Rancho Bernardo and Rancho Peñasquitos saw shifts in the number of registered Democrats over the past four years, allowing Democrats to outnumber GOP supporters in north inland and coastal areas of the county, data show.
Some of these areas have seen large population growth in recent years, and Hill said this may indicate the switch is due to residential mobility as opposed to voters actually switching parties.
“I’m sure it’s a little of both, but party registration switches pretty rare,” Hill said. “It’s most likely that young people and new residents are changing things over time.”
Four years ago, Republicans outnumbered Democrats by more than 1,400 voters in the 92009 ZIP code, an affluent area of southeastern Carlsbad. Today, the area‘s party advantage has flipped, and Democrats outnumber GOP voters by some 2,200 people.
About half of the area’s 48,900 residents are White, 31 percent are Asian, 11 percent are Latino and 2 percent are Black, according to data from the San Diego Association of Governments, or SANDAG. Some 61 percent of households had annual incomes of more than $100,000 in 2020.
Pitney said the trend seen among educated professionals may also explain the shifts in much of San Diego’s coastal regions. “These people with graduate degrees are more likely to be able to afford to live near the water,” Pitney said.
In southern Vista’s 92081 ZIP code, the number of registered Democrats rose by some 40 percent since 2018, data show. With Republicans gaining just 101 new voters in four years in the area, Democrats took control of the more rural area near San Marcos.
SANDAG data show more than half of the 33,200 residents are White, 30 percent are Latino, 8 percent are Asian and 4 percent are Black. Nearly 40 percent of the 11,000 households in 2020 reported an annual income between $45,000 and $99,000. Another 30 percent reported annual income below $45,000.
Other areas of San Diego County saw shifts in the number of voters registered with neither major party, leading to Democrats taking control.
Just one ZIP code in the county — 92055 in Camp Pendleton — shifted to a Republican majority, though the area has fewer than 300 registered voters.
In 2018, more than 35 percent of the 36,500 Mira Mesa voters in 92126 declined to identify with a major party — more than were registered with either party.
But since then, the ZIP code’s portion of registered GOP members remained relatively stagnant, while Democrats gained some 4,300 voters, becoming the area’s largest voter group.
SANDAG data show the area has the largest percentage of Asian residents among all ZIP codes in the county, with the group representing more than 36 percent of the 76,100 residents. About 34 percent are White, nearly one in five are Latino and 5 percent are Black.
Pitney said the overall trends seen throughout San Diego County indicate the area will likely lean blue for the foreseeable future.
Hill, of UC San Diego, said the voter registration data is a foundational tool for most campaigns when determining how to canvas and how many votes are necessary in specific areas to win an election.
“And based on these numbers, San Diego County Republicans are going to be heading into the mountains soon, because their opportunities are shrinking,” he said.
Despite outreach, the average voter age didn’t budge
Voter registration data show the average age of voters has remained stagnant at about 48 years old since 2010.
Despite dozens of campaigns over the past decade designed to encourage young people to take an interest in politics and countless foundations that help young adults register to vote, data show there are half as many 18-year-olds registered as there were in 2018.
Peter de Guzman, an associate researcher at the Center for Information & Research on Civic Learning and Engagement at Tufts University, said this may be due to the time voter registration databases were extracted by the registrar.
The Union-Tribune’s databases in both years were extracted in early October, and young voters are more likely to register and vote at the last minute.
De Guzman said there was also a larger-than-average surge in young adults getting involved in politics four years ago, which he attributed to the fatal shooting of two staff and 15 students at Marjory Stoneman Douglas High School in Parkland, Fla.
“Many young people were part of that gun violence movement and paid attention,” he said. “They were taking civic action, like volunteering and protesting, but it also led to them voting as well. It was a huge youth turnout election.”
However, de Guzman said the low number of 18-year-olds registered to vote in San Diego County is a departure from broader trends reported among young adults on a national level.
A study published Tuesday found that voter registration among people age 18 to 24 is up in more than two dozen states, including major electoral battlegrounds like Georgia, Arizona, Nevada and Michigan.
The study also found that California, Michigan and Kansas — three states with abortion-related measures on the midterm ballot — have some of the highest youth voter registration increases compared to 2018.
California‘s midterm ballot asks voters if the state constitution should be amended to protect a person’s reproductive freedom and prevent state interference in abortion and contraceptive use.
California also enacted legislation in 2018 to begin automatically pre-registering eligible 16- and 17-year-olds when they get their driver’s license or state ID, so that they are registered to vote as soon as they turn 18.