In an election being widely played out as a referendum on President Donald Trump, Southern California will play a key role Tuesday in Democrats’ efforts to win back a majority in Congress, with multiple local U.S. House seats considered to be up for grabs.

Nationally, Democrats need to win 23 seats from Republicans to tilt the majority in Congress in their favor. In the Southland, Democrats have their eyes on five seats — including two being vacated by Republican incumbents.

The bulk of the seats being targeted by Democrats are in the once-reliable Republican stronghold of Orange County, which has seen a liberal political shift over the years.

Two years ago, Democrat Hillary Clinton beat President Donald Trump in Orange County, the first time a Democrat won the county since Franklin Delano Roosevelt. That has encouraged Democrats, and for the first time the national organization has sent professionals to Orange County to help elect more Democrats to Congress.

In the 39th District in northern Orange County, Republican Rep. Ed Royce is stepping aside, and his vacant seat is being sought by Democrat Gil Cisneros and Republican Young Kim in a race considered to be a toss-up. Cisneros, a noted philanthropist, won a $266 million Lottery jackpot in 2010 and has injected $9 million of his own money into the race. Kim, a South Korean immigrant, worked for Royce for about 20 years before winning a seat in the state Assembly, where she served a single term. She is looking to become the first Korean American woman to win a congressional seat.

In the 49th District, which straddles Orange and San Diego counties and includes cities such as San Clemente and Oceanside, Republican Rep. Darrell Issa is stepping aside after an unexpectedly narrow reelection win two years ago.

Mike Levin, a Democratic environmental lawyer, and state Board of Equalization member Diane Harkey are running to replace Issa. Levin has never held political office, but he has served as the executive director of the Democratic Party of Orange County. Prior to sitting on the Board of Equalization, Harkey served in the state Assembly from 2008 to 2014, representing southern Orange County. She also served on the Dana Point City Council. Harkey received Trump’s endorsement in August and is a major backer of the campaign to repeal the state gas tax.

Republican Rep. Mimi Walters is being targeted by Democrats in the 45th District, which covers a wide swath of Orange County, including Irvine, Lake Forest and Mission Viejo. Walters has represented the district since 2014, and while the district has become more Democratic, she easily won re-election in 2016 — even as the district’s voters supported Clinton over Trump. She has continued to preach tax cuts, backing the Republican-engineered tax cuts. She is now facing a challenge from Democrat Katie Porter, a UC Irvine law professor who is critical of the Republican tax cuts and touts her role as a consumer advocate.

Democrat Harley Rouda, a real estate investor, is trying to unseat longtime Republican Rep. Dana Rohrabacher in the coastal 48th District in Orange County. Rouda, who portrays himself as a political moderate, is a former Republican who says he wants to protect health-care coverage and Social Security and Medicare. Rohrabacher, who has been criticized by Democrats for his close relations with Russia, opposed the Trump tax-cut package but backs the president’s vocal stances on immigration. Rouda has raised significantly more money in the race, saying he needs to spend heavily to have a chance at unseating a 15-term incumbent.

In the northern reaches of Los Angeles County, Democrats are putting their hopes in Katie Hill in her bid to unseat Republican Rep. Steve Knight in a district that stretches into Ventura County. The area is historically Republican, but 25th District voters went for Clinton in the presidential race two years ago, and recent polls show the race to be extremely close.

Knight is an Army veteran and former Los Angeles police officer who supported the Trump tax cuts and efforts to repeal the Affordable Care Act, known as Obamacare. Hill is a former executive for a homeless-services nonprofit agency, and she has expressed support for improvements in security on the U.S.-Mexico border and additional middle-class tax cuts.

Jeff LeTourneau, the vice chair of the North Orange County chapter of the Orange County Democratic Party, was bullish on his party’s chances.

“I think we’re feeling incredible,” he said. “We could sweep this thing, all four (congressional seats).”

LeTourneau predicted that turnout for an Anaheim ballot measure to increase the minimum wage increase for hospitality industry workers in the city may help boost Democratic candidates. He noted that due to newly registered voters, the 39th Congressional District now has a half-percent Democratic edge.

Orange County Republican Party Chairman Fred Whitaker said he was encouraged by the numbers of absentee ballots being turned in so far.

“I’m really pleased with the get-out-the-vote results of the weekend,” Whitaker said. “I’m very positive about the absentee ballot results so far. We’re looking forward to holding all of these (congressional) seats.”

Whitaker acknowledged “certainly a higher turnout than past mid-terms,” but, he added, “it’s not as high as the general (election). And if you take a look at our voters we’re getting our voters out for us. We’re pretty pleased with the trajectory.”

If turnout reaches general election levels, however, “Yeah, we’ll certainly worry,” Whitaker said.

“The demographics look really good” for Republicans, Whitaker said. “There is much more youth voting, but if you look at over 50 (voters) it’s really, really good.”

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