A surge in Democratic voter registration has cut Republicans’ advantage in Orange County to less than 6 percentage points and has doubled the number of Democratic cities over the past year.

The Republican margin has been shrinking since 1990, when the GOP edge was 22 points. But in the past six months, the pace of change has been four times as fast as the 26-year average – due in part to the GOP’s controversial presidential nominee. That could hurt the local Republicans in November’s down-ticket races.

“Donald Trump has become our best marketing tool,” said Henry Vandermeir, chairman of the Democratic Party of Orange County. “He’s insulted pretty much every constituency in this county, which has helped drive Democratic registration and turnout to new highs.”

Vandermeir’s registration efforts have gotten a boost from other quarters. In addition to the county Democratic Party, at least four left-leaning groups – including MoveOn.org – have been registering voters in Orange County. County GOP Chairman Fred Whitaker said his party has gotten virtually no outside help.

Additionally, Sen. Bernie Sanders attracted young adults who might have otherwise not participated. And the competitive Democratic presidential primary in June boosted turnout, while the Republican contest was already decided.

As a result, more Democrats than Republicans cast ballots in the county. And it was the first time in 48 years that more county ballots were cast for Democratic than Republican presidential candidates.

Importantly for legislative elections in Orange County, Trump’s effect on registration and primary turnout is likely to carry to November, boosting Democrats’ chances on down-ticket races, said Jodi Balma, a Fullerton College political scientist.

“He is the brand leader, and a lot of people don’t want to be associated with the party because of that,” she said. Also undercutting GOP motivation to vote in November is the absence of a Republican in the race to replace retiring U.S. Sen. Barbara Boxer.

“There’s not a big driving force to get Republicans to the polls,” Balma said.

But the GOP’s Whitaker doesn’t see a lot of top-of-the-ticket motivation for Democrats either.

“We expect to see an uptick in our (registration) numbers before November,” Whitaker said. “I just don’t see the excitement among their voters for Hillary.”

There are two close state legislative races where turnout could play a decisive roll: The state Senate race to replace termed-out Sen. Bob Huff, R-Diamond Bar, in the tri-county district where GOP Assemblywoman Ling Ling Chang is facing Democratic activist Josh Newman; and Democrat Sharon Quirk Silva’s challenge of incumbent Assemblywoman Young Kim, R-Fullerton.

It could also help Democrat Michele Martinez’s challenge of incumbent Republican county Supervisor Andrew Do. And Democrat Doug Applegate, who finished less than 7 points behind Rep. Darrell Issa, R-Vista, in the primary, is drawing attention from donors who see a chance for an upset of the incumbent, a Trump supporter.

Two wild card issues that could also affect turnout are whether ballot measures spur partisan turnout and whether backers of Bernie Sanders will bother voting, Balma said.

Young voters

Orange County was long touted as the nation’s most Republican county. The modern-era high point was 1990, when the GOP’s 56 percent share of the electorate translated to a 22-point advantage over Democrats. (In 1928, Republicans were at 73 percent.)

That edge has slowly dropped, to 17 percentage points in 2000 and to 11 points in 2010.

Republicans are now 39.7 percent of county voters, an all-time low. Democrats are at 34 percent, their highest since 1992. Voters with no party preference account for 22.6 percent, down from the all-time high of 23.6 percent last year.

That means Republicans’ 8-percentage point edge in February has shrunk to 5.7 points.

The long-term trend is largely due to shifting demographics. Latinos, who favor the Democratic Party over the GOP by more than 2-1, are 18 percent of the electorate and growing. And voters ages 18-34, who heavily favored Republicans in 2002, are now more likely to register as Democrats.

Republicans still prevail among voters in 24 of the county’s 34 cities, although the three biggest – Anaheim, Santa Ana and Irvine – are Democratic. In July, Tustin became the 10th city in the county to turn Democrat. That’s twice the total of a year ago. Fullerton is poised to follow suit, with the shrinking Republican advantage there down to 144 voters.

The other Democratic cities are Buena Park, Garden Grove, La Habra, La Palma, Laguna Beach and Stanton.

Balma anticipates the Democratic surge of the past six months will slow to closer to the 26-year average. At that rate, county Democrats would surpass Republicans in 10 years. Vandermeir also expects it to slow, but not until after the November election. He expects Democrats to be the county’s dominant party in three or four years.

Balma said Republicans have their work cut out for them.

“The Republicans really need to attract young people, and they need young people to run for office,” she said. “And it’s incumbent on Republicans to go after the culturally conservative and not assume they’re going to register Republican.”

Contact the writer: mwisckol@ocregister.com