In the spring of 2017, the Republican congressman from California’s Twenty-fifth District, Steve Knight, held a town-hall meeting in Simi Valley, a conservative, largely Caucasian bedroom community of Los Angeles, where Ronald Reagan is buried and where many Los Angeles Police Department officers sleep at night. Knight, who served eighteen years on the force, including some time on the controversial CRASH (Communities Resources Against Street Hoodlums) unit, is running for a third term, a bid that may be complicated by the fact that he has consistently voted with President Trump. Hillary Clinton won the Twenty-fifth—a large district with a rising Hispanic population and a lot of independent voters, which straddles parts of Los Angeles and Ventura Counties—by 6.7 points, in 2016. Knight won his last election, against a Democrat, by 6.2 per cent. The national Democratic Party, in its effort to regain the House, has targeted Knight’s seat as one to flip.

During a Q. & A. at the town hall, a young woman stood up. Speaking into a microphone held by one of Knight’s aides, she introduced herself, and people in the room began to whoop. “Last month, your party tried to overhaul the Affordable Care Act with the A.H.C.A.,” she said, referring to the American Health Care Act, the proposed “Trumpcare” plan, which the Congressional Budget Office estimated would render twenty-three million people uninsured over the next decade. “And I think your constituents made it very clear how they felt about the A.H.C.A., as people here can attest.” (Hundreds of residents of the Twenty-fifth District had protested outside of Knight’s office.) “As your constituent, I’d like to know,” she added, “why you didn’t stand up to Paul Ryan and the rest of your party to protect us from that horrible piece of legislation?”

Knight, pacing at the front of the room, muttered something about people in the fifty-to-sixty-four-year-old age bracket and asked, “I’m sorry, what’s your first name?” The audience guffawed.

“Katie,” the woman said.

If Knight’s ignorance was sincere—and clearly the crowd wasn’t buying it, at least not those sitting near in the vicinity of whoever posted video of the exchange online—it was the last possible moment that the posture would be remotely plausible. Katie Hill, who is thirty and a Democrat, had declared her run for Knight’s seat a few weeks earlier, on International Women’s Day, part of a wave of young women seeking elective office. (Margaret Talbot wrote about these candidates here in April.) Soon, with support from Emily’s List and endorsements from celebrities like Kristen Bell (“My girl Katie is running for Congress”), Hill was giving speeches at “retirement parties” for Knight and pushing out the hashtag #FlipItBlue. Hill and her staff—“the most millennial campaign ever”—were featured in a two-part documentary on Vice News Tonight on HBO. In the run-up to the primary, held last Tuesday, Hill outraised Knight. Now, having defeated the better-known Democrat, a former corporate lawyer named Bryan Caforio, she will face off against Knight on the November ballot.

Late last week, I spoke to Hill by Skype. She was back home at the small ranch in Agua Dulce which, a few days earlier, she’d been forced to evacuate due to a fast-growing brush fire: the day before the election, she was loading goats into a truck. Behind her, in the image on my screen, metal blinds were drawn, but harsh white desert sunlight leaked through anyway. Hill was in her p.j.’s, her hair pulled back in a day-off ponytail.

“You don’t know you’re part of a movement, that you’re going to be part of a groundswell,” she said. “There’s a great deal of responsibility being part of the forefront of it. I’m in one of the front-line races. I’m young, I’m a woman, I’m L.G.B.T.Q. I’m one of the California seats that’s going to be getting tons and tons of attention and I’m a new face for politics. We’re providing an inside look into what politics looks like in this post-Trump moment.”

Hill, a centrist Democrat, flouts the old identity conventions of female political contenders. She is married to a man, Kenny Heslep, but identifies as bisexual. (Knight, who has voted for discriminatory measures against L.G.B.T.Q. people, is the son of the late state senator Pete Knight, who was the author of California’s same-sex marriage ban. Pete’s son David married his husband in San Francisco, in 2004, when the gubernatorial candidate Gavin Newsom, then the mayor of San Francisco, defied the ban.) The bio on Hill’s Web site says that she and her husband have kids—“but of course by kids we mean their baby goats!” One of her campaign videos shows her free-climbing a hundred-foot tall boulder in the Angeles National Forest.

Hill grew up in the Twenty-fifth. In addition to prosperous middle-class-dream towns, such as Simi Valley and Santa Clarita, the district includes much poorer and more desolate communities, such as Antelope Valley and Lancaster, windblown outposts at the edge of the Mojave that are home to prisons and to the world’s largest solar photovoltaic power plant. Hill, whose grandfather went to college on the G.I. Bill, earned a full scholarship to Princeton for his graduate work, and became a political-science professor at U.C.L.A., has lived in both worlds. Her mother is an emergency-room nurse; her father is a Beverly Hills police officer. Voting for his daughter was the first time he had ever supported a Democrat.

When Trump was elected, Hill was leading one of the region’s largest homeless-services providers, PATH (People Assisting the Homeless), commuting from the ranch to PATH’s headquarters, in Silver Lake, each day. She and her colleagues had spearheaded a ballot measure to raise more than a billion dollars to fund permanent supportive housing for the homeless in Los Angeles. (The homeless population in L.A. is now thirty-four thousand.) The measure, known as Proposition H.H.H., passed, in the 2016 election, but Hill despaired. “Passing H.H.H. was this incredible victory,” she told me. “But instead of being able to celebrate, we realized what it meant to have a Republican House and Senate and Donald Trump as President—that that could undermine every bit of hard work we’d accomplished.”

Further Reading New Yorker writers on the 2018 midterm elections.

In a Facebook thread, a friend jokingly told Hill that she should run for office. She took the suggestion seriously. “Strategy was my role at PATH,” she told me. “Based on this energy around flipping the House, I wanted to be one of the first candidates to announce. I knew there was going to be a lot of energy around women because of the Women’s March, and I knew that getting early attention could be a big benefit. So three weeks after it was a nugget of an idea, I was all in.”

The blatant sexism in her own party took her by surprise. “From day one, you are questioned on your experience more than your opponents—your male opponents—even though, objectively, my direct experience is far more relevant than being a lawyer for large corporations,” Hill said. “Your age is questioned, even though Caforio is only a few years older than me. Your appearance is constantly under attack.” She went on, “I had so many people on the Democratic side tell me, ‘I’m sorry, I’d love to support you, but this is too critical of a race and I just don’t think a woman can beat Steve Knight.’ ” Her victory over Caforio in the primary has made those questions moot.

It seemed like the right time to ask her about her “resting bitch face,” an expression she referred to in the Vice documentary.

“It’s this,” she said, making her face still. Her mouth turned down a bit at the corners. She looked frank and self-assured, unapologetic. “It’s when you’re sitting with a relaxed face and people think you’re looking like a bitch,” she said. “I’ve gotten a lot of feedback that that’s the kind of face I have when I am thinking, or I’m being serious, or I’m trying not to roll my eyes at my opponents. We call it R.B.F.” There are strong signs that #RBF may be what is required to #FlipItBlue: a poll of voters in the Twenty-fifth District shows Hill defeating Knight by thirteen points in November.