California’s Darrell Issa, in a once-safe Republican seat, finds himself on the ropes

Solana Beach, Calif. • One by one, Doug Applegate's fellow veterans stepped up to the microphone and named the threat to America: Donald Trump. One of them shook with rage, discussing Trump's joke about the "captured" Sen. John McCain, R-Ariz. Others asked how Applegate's opponent, Rep. Darrell Issa, R-Calif., could support Trump and claim to be a friend of veterans.

"You have a presidential candidate insult women - you're talking about women who are for the first time being drafted," said Nancy Cook, 43, a Gulf War-era veteran, her voice quavering with emotion.

Just hours had passed since FBI Director James B. Comey's announcement that he would examine more emails to see whether Hillary Clinton had let classified information slip through her private server. Applegate, a retired colonel who has given Issa the first real challenge of his career, was sticking to the facts that had undergirded the challenge. Issa supported Trump, and the 49th District of California and its growing Latino voter base did not

"Demographics have changed in the 49th," Applegate said in an interview. "I knew this was a Marine district. I knew one thing the Democrats never have tried is to run a Marine. And I knt in the military, if you say anything that's racist or misogynistic, nine out of 10 times you'll be disciplined for it."

Every factor that cuts against Donald Trump's Republican Party cuts deeper in California. Last week, House Speaker Paul D. Ryan barnstormed the state's Central Valley to help incumbents who had won easily in 2014. This year, they would need to overcome more than a million new Democratic voter registrations - and a Trump candidacy that in one poll was cruising along with support from less than 30 percent of voters.

Four Republican-held seats in California are seen as competitive, all in large part Latino votes. In a decade, demographic change in the rest of the country could change dozens more seats that were thought to be safely red.

In ads and on the stump, Applegate asks voters to consider Issa a fumbling congressman and an apologist for the top of his party's ticket. He was, Applegate says, "Trump before there was Trump." Issa's years as Oversight Committee chairman, which included the first investigation of the 2012 Benghazi attack, are cited as proof that he has ignored the district.

Until the Comey letter, which prompted Issa to tweet that the FBI could "get it right this time," Issa's campaign has focused on problems with the Veterans Affairs hospital system and the National Guard bonus scandal. Most of Issa's lawn signs say that he is fighting for veterans; Applegate's signs eschew his first name for his title, colonel.

But it is the changing voter base, not any public campaign, that has Democrats salivating at the thought of beating Issa. Many of the new registrations came during Sen. Bernie Sanders of Vermont's ambitious but unsuccessful primary bid; more came after, helped by a Latino backlash to Trump and several well-funded campaigns to weaponize it. More came because of a new law that automatically registers voters when they obtain driver's licenses.

Applegate, 62, had never run for office, and the 49th District had never looked like fertile territory for a Democrat. Before 2011, and California's first nonpartisan redistricting, much of what became the 49th District was reliably Republican, with Camp Pendleton and the conservative "north county" of San Diego overwhelming the liberal towns on the Pacific coast.

"We assumed this race would be like the last few years, where we had well-intentioned candidates running in an unwinnable seat," said Francine Busby, the chair of San Diego's Democratic Party.

Ten years earlier, Busby found out why greater San Diego County was unwinnable, at least then. She ran three losing races for Congress; a close special election went against her when an opponent exploited an on-camera moment in which Busby told Latino volunteers they didn't "need papers" to support her. The Minuteman Project, which urged concerned - and armed - citizens to join slapdash border patrols, had a beachhead in the district.

Latino voters weren't coming out in numbers sufficient to challenge that. Many didn't register. Once, Busby recalled, a Latina candidate for local office in Escondido found that die-hard supporters forgot to cast votes because they didn't realize they needed to come out every time she was on the ballot.

"Every single year, people asked the same thing: 'How do we reach out to Latino voters?' " Busby said. "The Democrats are on the right side of the issues, but we'd never found a way to compel them to vote in great numbers. I knew we needed Latino organizers to make it work, and now that's happened. They're frightened about Trump."

This year, they've had help. Tom Steyer, the hedge fund manager who has poured money into pro-Democratic causes since the Citizens United Supreme Court decision, helped fund a campaign called "Yo Voy a Votar, ¿Y Tú?" - I will vote, and you? - supplementing what was on the ground. Patricia Serrano, chairwoman of the North County Immigration Task Force, said her group had registered nearly 1,000 Latino voters after a post-primary volunteer push.

Arcela Nunez-Alvarez, director of the National Latino Research Center at the University of California at San Marcos, said there had been fresh engagement on campus after Trump became a plausible presidential candidate. On the campus - built on old Mexican chicken farmland, Nunez-Alvarez pointed out - nearly 10,000 students walked past reminders to cast early ballots or join the Democratic Party.

"There's an interest in public policy I'd never seen before in north county," she said. "We have cities where the Latino population comprises half of the total, and 90 percent of the political representation is white."

New voters were among the thousands who turned out for the June primary - and made Democrats realize that Issa could lose. California's "two-step" system, in which candidates of all parties run in a primary and the winners advance, had never threatened Issa. This year, it gave him a narrow 5.3-point win. The Democratic Congressional Campaign Committee dove into the race, finding Issa in a tie for the general election.