IRVINE, California — A Democrat might finally have a real chance to win this congressional seat in Orange County. Even a candidate who endorses Medicare-for-all.

Katie Porter, a UC Irvine law professor, has a good shot at surviving California's "top two" primary on June 5 to take on Republican Rep. Mimi Walters in November. Porter's campaign touts a poll, fielded by a group that endorsed her, showing her beating Walters by 3 points in a hypothetical general election matchup.

Katie Porter, a Democrat running for the California 45th Congressional District, speaks to seniors in Laguna Woods on May 19, 2018.Bill Clark/CQ Roll Call

Walters first ran for Congress and won on conservative policies like repealing Obamacare here in Irvine in 2014. Porter, meanwhile, is running on a progressive agenda, including a push to move all Americans to a government-run health insurance program.

"What we see in the field, talking to voters, is that Orange County families are very concerned about the broken state of our health care system," Porter said at a recent forum for Democratic candidates. "The time is now to elect can-do Democrats who are going to fight for Medicare-for-all."

Walters's district, including Irvine and surrounding areas, has never elected a Democrat to Congress, but Orange County is changing. Hillary Clinton beat Donald Trump here by 5 points. The voters in this district are highly educated and increasingly diverse. Twenty-one percent of the population identifies as Asian and 18 percent as Hispanic, according to 2010 census data, and those numbers are likely even higher now.

President Trump listens to Rep. Mimi Walters (R-CA) (far right) speak before signing HR 1865, the "Allow States and Victims to Fight Online Sex Trafficking Act of 2017," on April 11, 2018.Chris Kleponis-Pool/Getty Images

Some Democrats have long thought the best strategy in places like Irvine, where Republicans have historically dominated, is to run moderate candidates who can peel off centrist voters. Porter's top challenger in what should be a neck-and-neck race, another UC Irvine law professor, Dave Min, fits that bill. He told me he worries a single-payer health care proposal is too far left for this community.

But this year, dozens of Medicare-for-all candidates, inspired by the populist politics of Bernie Sanders and Elizabeth Warren, are challenging that premise. They believe it's time for Democrats to draw a line over issues like health care, rather than try to inch Republicans toward the center.

Sen. Bernie Sanders (I-VT) speaks during a health care rally at the 2017 Convention of the California Nurses Association in San Francisco on September 22, 2017.Justin Sullivan/Getty Images

"I think there's a powerful counternarrative. It's about having the courage to engage with people on that," Porter told me.

It may be the biggest divide in this year's Democratic primaries. Last month, national Democrats backed a centrist ex-Congress member in his race against Medicare-for-all candidate Kara Eastman in Nebraska. But Eastman won anyway, and now she's charged with winning a crucial race for Democrats in November. Next up, a huge slate of Medicare-for-all candidates will test their message on June 5, California's primary day.

The Medicare-for-all candidates make their case: time for can-do, not can't-do, Democrats

The policy idea of "Medicare-for-all" is still pretty new to the national stage, but it's not new in progressive circles. The idea, as defined in bills from Sen. Bernie Sanders and other Democrats, is to move every American onto a government-run health care plan, which would cover almost every health care service at little to no cost when you get treated.

The days of private insurance, getting coverage through your work and Obamacare marketplaces, would be over. But that's the challenge that many health policy wonks see: namely, transitioning the 150 million Americans who get insurance through their employer into a new government health plan. The more moderate position is to simply bolster the insurance markets we have now, with a public option or more generous subsidies.

Porter — who worked with Warren previously and received her endorsement, plus that of Sen. Kamala Harris (D-CA) — has bigger ideas.

"The system we have, the status quo, is not acceptable," she said. "We're questioning whether we can rely on major players like health insurance companies to continue to be reliable partners in delivering health care."

Katie Porter speaks to seniors at the Laguna Woods Towers in Laguna Woods, California, on May 19, 2018.Bill Clark/CQ Roll Call

Porter believes it's important for Democrats to stake out an aspirational position. More than once, she talked about having a "can do" attitude instead of a "can't do" one. Without mentioning her opponent, she dismissed the idea of running on a more malleable "health care for everyone" message.

"It just sounds like oxygen for everyone," she says. "If we had this can't-do attitude, we wouldn't have Social Security."

Because it's California, Porter faces two other Medicare-for-all candidates: Brian Forde, an ex-Republican and ex-Obama White House official, and Kia Hamadanchy, who used to work for populist progressive Sen. Sherrod Brown (D-OH).

Min is most aligned with the Democratic establishment here, getting the state party's support, and he's the only Democrat not totally on board with single-payer. Then there's Walters, the sitting Republican.

From left: Dave Min, Katie Porter, Brian Forde, and Kia Hamadanchy, the Democrats running for California's 45th Congressional District seat in Congress, participate in a candidate forum in Irvine on May 22, 2018.Bill Clark/CQ Roll Call

Porter and Min are seen locally as the top candidates — though Forde has actually raised the most money, Hamadanchy has also built a credible campaign, and in a Democratic race with four first-time candidates, anything could happen.

Like many voters, Porter connects her personal story to health care policy. She described what she saw working as a consumer finance watchdog, families who had insurance but whose plans asked them to still spend thousands of dollars out of their own pocket and ended up bankrupt.

Even though the uninsured rate went down after Obamacare was enacted, it remains higher than other developed countries, and America's health care costs speak for themselves. Forde, the former Republican, told me he came to believe in single-payer after living under such a system in Nicaragua, where his asthma inhaler cost $7. In the United States, it cost $400.

"That is absurd," he said.

Still, this is a well-to-do district that already has a low uninsured rate. In focus groups Vox ran last fall on single-payer, even people sympathetic to the goal of universal health care were apprehensive at the thought of losing their own insurance. Polling shows that support for single-payer tends to drop when you talk to voters about increased taxes or government control of health care.

Porter knows she'd face attacks claiming that voters will lose their current coverage, that they may pay higher taxes, and about the government meddling in personal affairs. But she thinks she can craft a compelling counterargument.

"How much is your health insurance cost you now? How much does it cost your employer?" she said. "We need to be able to say, 'You won't have to worry each month, choosing between your health insurance and choosing your rent. You'll never go broke.'"

Other Democrats ask: is it too risky to go full single-payer in a red district?

Min is accused, if you want to call it that, of being the establishment moderate in this race. He answers a lot of questions with an apology about how nerdy he's about to get. When I ask him about automatic voter registration, he begins with the ancient Greeks.

Min, like the other three Democrats, is a first-time candidate. He's reluctant to support Medicare-for-all right now, saying he thinks a more modulated message is necessary in this district, which is almost evenly divided among Democrats, Republicans, and independents.

The idea, he says, is "very, very open to political attack." And the time frame for implementing it under, say, the Sanders bill is "unrealistic," risking disruption for the kind of people who live in Orange County and might be happy with the insurance they have right now. (The Sanders plan would move every American to a new government plan over four years.)

Dave Min, Democrat running for California's 45th Congressional District seat in Congress, speaks with supporters in the parking lot of El Toro High School in Lake Forest on May 20, 2018.Bill Clark/CQ Roll Call

Then you have the costs and the potential for higher taxes, even if people would no longer have to pay insurance premiums either.

"People here are very, very sensitive to tax burdens," he told me.

Instead, Min thinks he can win by getting Romney Republicans as part of his potential voter coalition. As we walk through a neighborhood of vaguely postmodern houses and indistinct culs-de-sac, he seems to find an audience for his pitch while navigating away from the more explosive single-payer issue.

Deborah Rothbart is a 64-year-old who says she's a registered Democrat but understands the saying that you get more Republican the older that you get. She's about to go on Medicare. She mentions the "one-payer issue." Min deftly pivots to preserving Medicare as it exists today.

Dave Min speaks with Deborah Rothbart, 64, on the campaign trail in Irvine.Dylan Scott/Vox

Jonathan Resnick, 57, buys Obamacare-compliant coverage off the marketplace. He says the cost just increased from $1,200 to $1,500, and he makes too much money to get federal assistance. But when Min mentions single-payer, Resnick doesn't seem too into it. So Min talks about the way he wants to improve the existing market by introducing a public option and by letting Americans over 55 buy into Medicare.

"I think there's a distinction here between goals and means," Min told me over coffee. "Single-payer is one way of getting there, but it's a far leap, and if single-payer becomes a detriment to getting to universal coverage, then I think you're doing yourself a disservice."

The Democratic debate in Orange County, and others like it, will define the party's future

Democrats have the opportunity to win a wave election this fall. But to do it, the party will need to pick up seats in traditionally Republican-held districts, in places like Irvine.

All over the United States, Democratic primary voters are being asked to choose between their heart and their brain, as one local Democratic leader put it to me. Do they vote for the policies they really believe in — like Medicare-for-all, which is now a majority position within the party? Or do they vote on electability, knowing Republicans will pummel a single-payer advocate as just one more tax-and-spend Democrat?

Sens. Elizabeth Warren (D-MA) and Bernie Sanders (I-VT) discuss Medicare-for-all legislation on Capitol Hill on September 13, 2017.Jim Watson/AFP/Getty Images

The Sanders-Warren wing is ready for the fight, believing that health care is a unique issue for American voters. Polling indicates that the public is increasingly comfortable with a major government role in guaranteeing health care.

"People need to see us legislate in a way that affects their lives," said Hamadanchy, who also pointed out he was the first Democrat in the race to support single-payer. "The Democratic Party needs to stand for something that's not just being against Trump."

At the same time, in well-off districts like Walters's that lean Republican, a lot of voters get pretty good coverage through work. The uninsured and Medicaid rates are low here. And roughly one-third of voters decline to publicly register with either party. A Democrat needs those voters if they're going to win.

Volunteers work the phones in the new National Republican Congressional Committee field office in Irvine, California, on May 22, 2018.Bill Clark/CQ Roll Call

Teri Sorey, the vice chair of a local PAC aimed at getting Democrats elected in Orange County, sees it both ways. On the one hand, she's a bit dismissive of Min's more incremental platform — "he says we need to improve things, but I'm not sure exactly what he means" — but on the other, she is conscious of the electability issue in a district that FiveThirtyEight called a bellwether in the Democratic pursuit of House control.

"Where are they going to get their winning votes?" she said. "Those might be the people who aren't quite ready to go full single-payer."

People here tell me there is a lot of energy among Democrats. Still, winning won't be easy: I heard from one person that they thought this district would be competitive in 2020, not 2018. But Trump is just unpopular enough that Democrats might have a chance to win now.

But first, they have to choose their candidate. Min isn't there yet on single-payer. He thinks the goal of universal health care is more important than the means. Porter, on the other hand, believes that Medicare-for-all, in a country where medical bankruptcy can still destroy people's lives, can win anywhere.

It's an important distinction, maybe the most meaningful policy decision voters are being asked to make in this race. Because there is one thing all four of the candidates agree on: Democrats need to win in November.

Trump supporters during a campaign event in Orlando on November 2, 2016.Jabin Botsford/The Washington Post via Getty Images