Los Angeles • On a recent Sunday evening, Katie Hill, 30, whose father is an L.A. police lieutenant in Beverly Hills, boarded a red-eye flight to Washington for frenetic fundraising and networking. She must really want to get into the House of Representatives. If she does, she will have defeated a two-term incumbent, Rep. Steve Knight, 51, who was an L.A. police officer for 18 years and is the last Republican in a district containing a significant portion of Los Angeles County.

California’s 25th District includes Simi Valley, which is famous as the home of the Ronald Reagan Presidential Library and the trial of police officers charged with brutality against Rodney King. It is home to many of the Los Angeles police officers who helped quell the city rioting after the accused officers’ acquittal. Hill’s father-in-law, too, is a cop. Her husband’s uncle was an officer killed in the line of duty; his death is currently Orange County’s only unsolved police murder. In the June 5 primary, Hill will be the first Democrat to receive her father’s vote.

The 25th is at the top of the list of seven (of 14) Republican-held California seats that Democrats hope to capture because Hillary Clinton carried them. The seven are almost a third of the 23 such districts nationwide. Joe Trippi, the Democratic consultant who was media adviser to Doug Jones’ successful Alabama U.S. Senate campaign, says Jones got votes from Republicans who still support the president but want no more chaos. But referring to California Democrats, he warns that “our own enthusiasm might get in the way.”

This is because in 2012, Democrats — who run this almost monochrome blue state — ignored the axiom that improvements often make things worse. They instituted a primary system under which the top two vote-getters for an office are on the November ballots, even if both are from the same party. This year, Democrats, fueled by fury against the president, might produce such a profusion of candidates that the Democratic vote will be fragmented, putting weak general-election Democrats, or no Democrats, on some November ballots.

In 2014, when Republican Buck McKeon, chairman of the House Armed Services Committee, retired after 11 terms representing the 25th, Republican Tony Strickland, with 30 percent of the primary vote, ran against Knight (28 percent) in November. Democrats were excluded because their top performer in the primary received 22 percent. In 2016, a Democrat, Bryan Caforio, ran against Knight and lost by 6 points while Clinton was winning the district by 7 points. Caforio is running again. Either he or Hill probably will be Knight’s opponent in November.

Congressional districts drawn by Republican state legislatures after the 2010 census and after that year’s anti-Democratic wave election might somewhat insulate Republicans from a “blue wave” this year. But eight years is a long time in a dynamic region like Southern California, and for eight years the 25th has been receiving an influx of “housing refugees” — people of modest means seeking affordable housing outside the city, and bringing the city’s political sensibility. The district is now 39 percent Latino.

Donald Trump, who did not visit California in the 13 months after becoming president, did worse there in 2016 (31.6 percent of the vote) than Herbert Hoover did against Franklin Roosevelt in 1932 (37.4). Yes, Hoover was a California resident, but the national unemployment rate was 24.7 percent. The district is more than one-third Democratic, about one-third Republican, and one-quarter independent. Knight’s vote for the Republican tax bill, with its limits on the deductibility of state and local taxes, adds to his vulnerability in high-tax California.

Being 21 years younger than Knight is another Hill advantage. In 2008, Barack Obama carried national voters under age 45 by 15 points. In Alabama in December, Jones carried that age cohort by around 20 points. Suburban women, of whom the 25th District has many, also are recoiling against Republicans. The Economist reports that, nationally, “around 400 women, mostly Democrats, are planning to run for the House, at least 50 for the Senate and 79 for governor. ... At state and local levels, the picture is the same. In 2015 and 2016, around 900 women consulted Emily’s List [which supports women candidates] about standing for office; since Mr. Trump’s election, over 26,000 have.”

One of them recently took a red-eye to get on Emily’s List.