San Juan Capistrano, California (CNN) After a 2018 Republican wipeout in Orange County , San Juan Capistrano Mayor Brian Maryott is betting that his record as "a quiet leader" can help turn the GOP's congressional fortunes around in Southern California.

That was the message Maryott delivered to a group of three dozen Republicans at a hilly country club home on a recent Sunday afternoon, as he prepares to challenge freshman Democratic Rep. Mike Levin. Maryott didn't criticize President Donald Trump -- in fact, he and numerous attendees touted Trump's record -- but the mayor's message still drew a clear contrast with the Republican who will be at the top of the ticket in 2020.

"I'm a quiet leader in our city. I said there were some things I was going to do, I was going to take the temperature down in city politics," Maryott said. "Most people don't associate with me this big thing or that bad thing or anything else because I've been a quiet leader in the city, an effective leader. And that's what I want to do in Washington."

Maryott is one of the many Republican challengers looking to win back the seven seats in California that Democrats flipped in 2018 when they swept into the House majority. Nowhere was the Republican pain more acute than in Orange County, the longtime stronghold of Ronald Reagan Republicanism, where Republicans lost all four of the county's six districts they had held.

The Orange County seats are seen as key battlegrounds if Republicans have any chance to take back the House majority next year.

"They have to try to figure out across the country how to get the 18 seats back to take the House back," said Fred Whitaker, the chairman of the Orange County Republican Party. "I think that path has to go through California, and I think it's going to go through Orange County."

But Republicans face an uphill climb.

San Juan Capistrano Mayor Brian Maryott is challenging freshman Democrat Rep. Mike Levin for his Orange County US House seat.

Long-term demographic shifts and an influx of tech jobs have gradually turned Orange County more Democratic, as it has become younger and more diverse. The four Democratic freshmen in Orange County -- Reps. Katie Porter, Harley Rouda, Gil Cisneros and Levin -- will enjoy the built-in advantages of incumbency, including a two-year campaign runway and the chance to build a record of work for the district.

And perhaps most importantly, Trump's unpopularity could continue to drag on Republicans.

"The President is just horrifically unpopular," said Fred Smoller, a political science associate professor at Chapman University in the city of Orange. "Because Orange County Republicanism is really a libertarianism. The Republicans here want lower taxes, they want less government regulations, they want more local control. They find the anti-gay, anti-women's choice, anti-environment really doesn't fit."

Democrats outnumber Republicans

In a sign of the county's shift, the number of registered Democrats eclipsed the number of registered Republicans last month, and Democrats now have a roughly 4,000-voter advantage , according to data from the Orange County Registrar of Voters.

To Levin, who was executive director of the Orange County Democratic Party more than a decade ago, the change is remarkable.

"We dreamed about the day when we would have more registered Democrats," he said in an interview.

Levin, whose coastal district spans Orange and San Diego counties, cited a combination of factors, including the tech sector and voters' environmental concerns, for the Democratic gains. But he also noted Republicans still outnumber Democrats in his portion of Orange County, a sign that his campaign will be no cakewalk.

"We can't be complacent. We can't take any of these seats for granted," he said. "Each of us that worked so hard to flip the county need to stay focused, and we've got to continue to build upon the success we had in 2018."

To Republicans, the 2018 election was a surprise -- but they also argue it was an anomaly.

They say Democratic donors poured money into the Orange County congressional races in 2018, and in 2020 they will have a level playing field with big donors focused on the presidential contest.

"I think the last election was a super anomaly to have that kind of money spent, where they could spend it across the board," said former Rep. Buck McKeon, a California Republican who retired from Congress in 2014. "The presidential election, nationally, I think they'll soak up all of that money that went to the congressional districts and the Senate last time."

Whitaker said the most important voter-registration shift hasn't been toward Democrats, but rather voters who state no party preference. They now represent 27% of Orange County's registered voters.

"We can't take it for granted, and I think for years we did that: The Republicans would come out and vote and keep it Republican," said Greg Raths, the mayor of Mission Viejo, who is one of several Republicans vying to challenge Porter. "But we've got our work cut out for us. ... I think it's going to be a tough, close race."

Running on a record

The Democrats who flipped Republican seats in 2018 ran against the President and Republicans' control of Congress, but now they will have to campaign on their own records.

At town halls over the summer recess, Democratic freshmen have been quick to tout the bipartisan legislation they've helped pass and work they've done with Republicans -- while blaming Senate Majority Leader Mitch McConnell for the gridlock on larger issues like health care, immigration and guns.

When Rouda was asked at a recent town hall whether he thought Congress would do something on gun control, he bluntly said no. "The fact we have too many politicians who won't do what the public wants because they're in the pocket of the gun lobby tells you what's wrong with Washington, DC," he said.

Rep. Katie Hill, a freshman Democrat who flipped a northern Los Angeles district in 2018, said the inability to pass high-profile legislation made on-the-ground district work even more vital.

"I don't think any of us were delusional in thinking that we would be able to go in and pass these massive health care bills that we campaigned on," Hill said in an interview. "People in these front-line seats, in particular, are acutely aware that our jobs depend on us doing a good job and being effective representatives."

But Trump is still a key focus for those Democrats. And in California in particular, Trump's tax cuts are front and center, after the law's cap on deductions of state and local taxes hit high-tax states like California particularly hard.

"The President was clear he did it to be punitive to certain people," Porter said at a town hall last month. "You passed taxes that blew up our deficit but politically punished certain states and certain areas that are making it hard for local and city governments to fund services we desperately need."

Combating the Trump effect

Republicans say they can make Orange County red again because Trump won't have the same drag that he did in 2018.

"Because our President's name was not on the ballot in the 2018 cycle, you saw a lot of people ... let out their anger and frustration by voting against any and all Republican candidates," said Young Kim, who narrowly lost in 2018 to Cisneros and is challenging him again. "In 2020, because he will be on the ballot, they have a choice, and there will be a lot of split voters."

Kim, who would be the first Korean American in Congress, argued that the President's strong economy and her message of Republican opportunity would combat any anti-Trump sentiment.

Maryott walked the line while taking questions from supporters to note that Trump was not a normal politician but still got things done.

"The President is pretty bombastic. And he probably registers a little bit on the narcissistic scale -- a pinch, anyways. But he's a doer," Maryott said to laughter and applause. "He's created some unique challenges, but he's also created some unique results."

Still, Maryott made sure to note where he disagreed with the administration, such as offshore drilling, and he accused both parties of "lobbing spitballs at each other" instead of solving the country's immigration problems.

Republicans are also looking to the economy, which remains strong despite some warning signs, predicting that voters will be more concerned about that than the President.

"All the Democrats, they want to focus the attacks on the President and impeachment, to avoid talking about the fact that nothing has been done on kitchen-table issues," said Peggy Huang, a Yorba Linda city councilwoman who's among the Republicans challenging Porter. "When people have to make a choice between paying for medical bills and putting food on the table or whether the President is impeached or not -- those are the issues I'm talking about."

Could impeachment change the landscape?

As the Judiciary Committee moves forward with its impeachment investigation , the Republican campaign arm is ramping up its attacks on Democrats over the issue, while some front-line Democrats are getting more vocal in their opposition.

Of the seven freshmen Democrats in California who flipped GOP seats, three are publicly supporting an impeachment inquiry , while four are not.

Those backing an inquiry have faced criticism. Maryott, for instance, argued against "more chaos in politics," but he used the line to criticize Levin, not Trump, citing impeachment and even Twitter.

"Unfortunately our incumbent is tweeting a couple times a week, he's bashing the President, he's voting for impeachment, as you know," Maryott said. "He has no respect for Republican opinions. ... We need to partner with the administration, not fight 50 lawsuits."

Levin has distinguished between supporting an impeachment inquiry and impeachment itself, but he acknowledged the issue could open Democrats up to political attacks, arguing that the President's conduct can't just be ignored.

"I think people are deeply concerned about the future of our democracy, about the rule of law. Clearly, I appreciate the diversity of opinion out there," he said. "I'm just going to keep at it. And I hope they will evaluate my service on what I've done for our district, and hopefully understand the tough decisions that we make."

A member of 'The Squad'?

Ayanna Pressley of Massachusetts and Rashida Tlaib of Michigan. While Democrats look to tie their Republican opponents to Trump, Republicans want to connect Democratic freshmen to their colleagues in "The Squad" : Reps. Alexandria Ocasio-Cortez of New York, Ilhan Omar of Minnesota,Ayanna Pressley of Massachusetts and Rashida Tlaib of Michigan.

Huang, for instance, criticized Porter over Ocasio-Cortez's Green New Deal , claiming that it would wipe out technology jobs in the district, although Porter has not co-sponsored the legislation.

And at a town hall last month, Levin was pressed by an attendee who said, "What's going on with 'The Squad' is repulsive," and that he had left the Democratic Party because of anti-Semitism.

"I called out anti-Semitism when members of my own party said it; I called out anti-Semitism when the President said it," responded Levin, who was raised both Jewish and Catholic.

Maryott pointed to Levin's membership in the Congressional Progressive Caucus to knock him as an "open borders Democrat" and said Levin supported a "100% government takeover of health care," two areas that Republicans are likely to focus on in 2020 as the presidential race pushes the Democratic Party leftward on those issues.

Rouda was pressed by a town hall attendee about Democrats supporting open borders, but he pushed back.

"First of all, Democrats don't believe in an open border," Rouda said to applause, arguing that Democrats had a better immigration record on immigration because the GOP refused to take up the Senate's 2013 compromise legislation.

in the freshmen class for Porter, who has gained plauditsin the freshmen class for her sharp questioning of JPMorgan Chase CEO Jamie Dimon , subtly distanced herself at her town hall from Democrats who have proudly said they are socialists.

"I'm a real champion for capitalism. What we need is capitalism that creates opportunity," Porter said, noting that Dimon had become her "pen pal" after their April exchange.

Smoller, of Chapman University, said that while Trump remained unpopular in Orange County, the Democratic choice at the top of the presidential ticket could ultimately play a significant role in the fate of close congressional races.

"The polling is telling us that the American people don't care for Trump, but, boy, they do not want a socialist on the Democratic ticket," Smoller said. "If you do get too far to the left, the Democrats could shoot themselves in the foot."