YORBA LINDA, Calif.— Democrats' long-predicted blue wave of support in California propelling the party into the House majority is not showing up in early voting in most of the state's targeted districts, offering GOP candidates a sign of hope in the last days of furious campaigning.

Political data expert Rob Pyers of the nonpartisan California Target Book keeps close tabs on early ballot return numbers provided by Political Data Inc., the state's most reliable political number-crunching firm. Late last week, Pyers said he was surprised to see some figures in key races that he noted "should concern Democrats."

In California's June primary, Democrats turned out at higher rates than Republicans in three of the seven districts Democrats are targeting in the state, the contests for control of California's 4th, 48th, and 49th districts. In those same districts, he said, the early voting "proved to be somewhat prophetic" because Democrats had returned a greater percentage of their mailed ballots than Republicans.

However, in the general election, the ground has shifted with GOP mail ballot returns outpacing those of Democrats in the same districts—as well as most of the hotly contested congressional races throughout the state.

Statewide, Republicans are running 1.39 percent ahead of Democrats in the ballots they have returned, with the widest GOP margin occurring in California's 21st Central Valley district where Democrat TJ Cox is trying to unseat Rep. David Valadao (R., Calif.).

Matching the Republican voting edge in the primary, 28.5 percent of the ballots mailed to GOP voters have been returned in the 21st district compared to 18.9 percent of those sent to Democratic voters, Pyers said. A September poll had Valadao with a 10-point lead over Cox.

More Republicans tend to vote early in California elections across the state so it's too early to tell if the mail-in ballot edge will have an impact in the final ballot counts. Pyers late last week also tweeted out figures showing an ongoing downward trend for Republican voter registrations.

Registered GOP voters across the state and in several key districts have continued to dwindle as voters identifying as independents and Democrats have increased their rolls this cycle. In Orange County, Pyers said the GOP voter registration advantage had slipped from 3 percentage points in the June primary to just 1.16 percent.

Republican candidate Young Kim, who is running neck-in-neck against lottery winner Gil Cisneros in Orange County, one of the nation's closest House races, said she is leaving nothing to chance in the final days.

"I have four events today," she told the Washington Free Beacon Saturday after participating in a gas-tax repeal rally outside her Yorba Linda campaign office. "The excitement is there, the students [at an event today] are saying that their parents are already voting for me. This is a really good feeling for me."

Kim, who served in the state assembly and as a staffer for Rep. Ed Royce, said it's not surprising that Republicans are doing better in early voting.

"This is the midterm election cycle so typically Republicans do better in terms of voter turnout, especially in the absentee voting turnout," she said.

Kim says her status as a Korean-American immigrant in a district where roughly two-thirds of the voters are Asian or Latino is attracting enthusiastic support. However, it's her longtime commitment to the district that she expects will put her over the finish line.

"I have served in this community for over two decades with Ed Royce. I also served in Sacramento so people are used to having my name, not only on the ballot but as someone who is visible and always connected in the community and always grounded in the community," she said.

Retail politics plays a decisive role in California politics where undecided voters tend to make up their minds just days before the election.

Still, the Republican early voting edge is surprising strong in several races, even in California's 49th district where some recent polls have Democrat Mike Levin leading GOP opponent Diane Harkey by double digits while the latest, released Friday, said the gap has tightened to 7 points.

In that contest, as of Sunday, 46,000 Republicans had returned their ballots compared to 38,000 Democrats and 28,000 independents, according to California Target Book tallies.

In tighter races, Republicans have also outpaced Democrats in early voting. In the Kim-Cisneros contest, 33,000 GOP voters mailed in early ballots compared to 25,000 Democrats and 18,000 independents.

Six of the closest congressional races are taking place in Southern California with three in the heart of Orange County and one stretching from Orange County into North San Diego County. In the past, these districts were considered GOP strongholds, but all four voted for Hillary Clinton over Donald Trump in the 2016 presidential race.

Even so, late polling is giving at least one Republican the edge in the final homestretch. Rep. Steve Knight (R., Calif.), the only Republican House member in Los Angeles, has a four-point lead over Democratic challenger Katie Hill, a Siena College and New York Times poll found.

Roughly 24,000 Republicans mailed in their ballots in that district compared to 22,000 Democrats and 13,000 independents.

Several other Orange County Republicans are running neck-in-neck with their Democratic opponents and like Kim are arguing that their local ties and longtime district presence will help attract voters to their side.

Rep. Mimi Walters (R., Calif.) is two points behind challenger Katie Porter, who is running a liberal campaign, while longtime Rep. Dana Rohrabacher (R., Calif.) appears to have carved out an edge against Democratic challenger Harley Rouda, although the two were exchanging the lead throughout the final weeks of the campaign, according to recent polling.

As of Sunday, 52,000 Republicans voters in the Walters-Porter race had returned their ballots early compared to 39,000 Democrats and 31,000 independents. In the Rohrabacher-Rouda contest, 53,000 Republicans mailed in their ballots early, compared to 39,000 Democrats and 29,000 independents.