Former President Barack Obama speaks to students at the University of Illinois where he accepted the Paul H. Douglas Award for Ethics in Government on September 7, 2018 in Urbana, Illinois.

Democrats appear hopeful of gaining some GOP-held House seats in California in the November midterm elections. But a campaign rally planned for Saturday with former President Barack Obama may say a lot about what obstacles remain for them in flipping traditionally red congressional districts that President Donald Trump won in 2016.

All seven of the congressional candidates expected to join Obama at the rally in Anaheim are from Republican-held districts that Democrat Hillary Clinton won in the 2016 presidential election.

Yet several districts that Trump won have GOP incumbents seen as vulnerable and Democratic challengers rising in the latest polls. But Democratic candidates in those other districts were not invited to participate in Saturday's rally.

The Democratic Congressional Campaign Committee, which organized Saturday's event, stood by its decision to have just the seven candidates, but a spokesman didn't elaborate.

The GOP has a 23-seat majority in the House. However, Democrats are hoping to pick up enough GOP-held seats in California and other close races around the nation to wrest back control of the chamber they lost in the 2006 midterm elections.

During a speech Friday in Illinois, Obama called for Americans to vote in November, saying "our democracy depends on it." Obama also said his successor, Trump, is "the symptom, not the cause" of division in the nation.

Democratic candidates scheduled to attend Saturday's rally include Josh Harder, T.J. Cox, Katie Hill, Gil Cisneros, Katie Porter, Harley Rouda and Mike Levin. Five of the seven are from Southern California districts, while two are from the Central Valley region that historically has skewed conservative.

Still, there are other districts in the state where GOP incumbents have seen Democratic challengers rising in the latest polling. They include the Central Valley-based 22nd District, where Democrat Andrew Janz, a local prosecutor, is facing off against Republican Rep. Devin Nunes.

Nunes, an eight-term incumbent who chairs the House Intelligence Committee, may be starting to lose some support in the district due to distractions. Those distractions include the Trump-Russia investigation and what one local newspaper last month called a "list of unflattering Nunes news events over the summer," such as using campaign donations to purchase Celtics tickets and personal trips.

The latest polling shows Nunes ahead by 5 percentage points against Janz, according to a poll conducted in late July of 400 likely voters in the district by Democratic polling company Tulchin Research. By comparison, a poll conducted shortly after the June primary by Public Policy Polling, a left-leaning polling firm, found Nunes with a wider, 8-point lead.

Experts consider Janz the strongest challenger Nunes has faced since he went to Congress in 2003. They say Janz has been able to create a larger base of support and more fundraising capabilities and could benefit from Hispanic voter turnout and Democratic-leaning independents in November.

Even so, Janz wasn't included in the Obama campaign rally. Obama also hasn't endorsed him for the congressional race.

Heather Greven, a spokesperson for the Janz campaign, was contacted for this story and referred calls to the DCCC for comment on why the Central Valley candidate wasn't invited to the Anaheim rally.

"We are staying focused on talking to voters in CA-22, not jet-setting to and from fundraisers across the state," Greven said in an email response.

Then again, Obama won California in the 2008 and 2012 presidential elections but lost several districts in the lower Central Valley, including the 22nd District, to Republican challengers. Agriculture is a leading industry in the San Joaquin Valley, and water is a hot-button issue. Some farmers blame Democrats and environmentalists for diverting water to protect endangered fish rather than to help grow crops.

As president, Obama offered some drought relief for agribusiness in the Central Valley, but some farmers insisted it didn't go far enough.

Another Republican incumbent slipping in polling is Rep. Duncan Hunter in the San Diego County-based 50th District. Democrat Ammar Campa-Najjar, a business owner, has been gaining in recent polling amid Hunter's legal problems over allegedly using campaign funds for personal expenses.

A Tulchin poll reported this week showed the embattled five-term congressman essentially tied with his challenger Campa-Najjar. Both had 46 percent in the internal poll conducted for the Democrat, while the undecided number was 8 percent.

A SurveyUSA poll before the June primary had Hunter leading by more than 30 points against Campa-Najjar. The incumbent won re-election in the 2016 general election with nearly 64 percent of the vote and defeated a challenger in 2014 with more than 70 percent of the vote.

On Saturday, a spokesman for Campa-Najjar's campaign told CNBC the former president's office had "personally invited" the candidate to attend the Anaheim event "as a special guest."

Trump won the 50th District in 2016 against Clinton, but Obama carried it in 2008 when he ran against the late Sen. John McCain, a Republican from Arizona.

-Updated with comment from campaign of Democratic congressional candidate Ammar Campa-Najja.



