Dan Ardell has been voting Republican all his life, but not this November.

In many ways he is a conservative from central casting: a churchgoing 77-year-old retired businessman from Orange county, the suburban expanse between Los Angeles and San Diego that was once said to be where good Republicans went to die.

Ardell voted for Barry Goldwater over Lyndon Johnson, Ronald Reagan over Jimmy Carter, and George W Bush over Al Gore. But now he has had enough – enough of Donald Trump, certainly, but also enough of Dana Rohrabacher, the beguilingly soft-spoken but reliably out-there rightwing congressman who in 30 years on Capitol Hill has never previously faced a significant election challenge.

“Rohrabacher is of the same caliber as Trump,” Ardell said. “They’re low-level, relatively unintelligent people. Trump has no civility, no common sense. He can’t even spell the word nuance.”

Ardell’s list of grievances goes on: how Trump and modern-day Republicans have erased any pretense at fiscal responsibility, how they are destroying America’s international alliances and wiping out global trade. “There is no more Republican party,” he lamented. “With Trump, it’s gone.”

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One might think such views would make him an outlier in a district represented by Rohrabacher, a cheerleader for both Trump and Vladimir Putin who believes America should not tolerate undocumented immigrants or offer a path to citizenship, sees Barack Obama and Hillary Clinton as enemies of the US, believes climate change is a “total fraud” and thinks property sellers should be allowed to turn away homosexual buyers.

In fact, Ardell is part of a growing trend of disaffected Republicans along Orange county’s coastal strip, an area of yachting marinas and country clubs, strip malls and cookie-cutter housing estates in the hillsides overlooking the Pacific Ocean. Many of them have spent their lives identifying with the GOP – pro-business, suspicious of high taxes and regulation, strong on law on order – but now they are tired of the rancor and the classlessness emanating from Washington and looking for a new political home.

“There’s a lot of people like me,” Ardell says. “A ton of ‘em.”

Facebook Twitter Pinterest California could play a determining role in upsetting Republican control the Congress. Photograph: David McNew/Getty Images

That disaffection presents a golden opportunity to Democrats and explains why California’s 48th congressional district is right at the top of the party’s hit list as it seeks to retake control of the House of Representatives in November’s midterms. The opportunity is not just to bloody the president’s nose and send one of Washington’s quirkier representatives packing: it is to effect wholesale political change in a district once thought to be impervious to it.

Harley Rouda, the real estate magnate turned Democratic party challenger to Rohrabacher, is a former Republican. So are many of the locally hired staff and volunteers on his campaign team. The number of registered Republicans in the district is steadily diminishing, down to around 40% now compared with 44% four years ago, while the number of registered Democrats and those designated “no party preference” is steadily increasing.

“There’s a cultural shift,” said Katherine Amoukhteh, an engineer who has been a registered Republican for 20 years but is supporting Rouda. “The party has changed a lot ... and that’s left us with one of two choices. Either we say, to hell with you guys and become Democrats or independents. Or we stay on the team and say, I may be a Republican but I don’t have to vote Republican up and down the ballot.”

Amoukhteh hated the way Trump talked about women on the campaign trail and refused to vote for him. Then she looked at Rohrabacher and found she could not abide him either. “My litmus test was Roe v Wade,” she said. “How can we still be talking about whether women have abortion rights? I have a teenage daughter. I want to be able to look her in the eye and say, ‘I did the best I could.’”

As is common in many affluent suburban districts, it is Republican women who are leading the charge. Two of them, both now Rouda supporters, told the Guardian of the existence of secret wives’ clubs in Newport Beach whose members loathe Trump but have not dared tell or confront their husbands. These women meet in each other’s homes – many of them in the desirable Port streets overlooking Newport Bay – to talk politics, but won’t be seen together in public and won’t canvas or phone-bank for Rouda for fear of being found out.

“Sometimes I think we should go around with T-shirts saying, ‘I’m married to a Republican’,” said Amoukhteh, who belongs to a non-secret group called Women for American Values and Ethics, or WAVE, that has grown from just a handful of members to 700 over the past 18 months.

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The 48th district is one of four in Orange county – and one of seven across California – that returned a Republican congressman in 2016 but also favored Clinton for president over Trump. Rohrabacher is the most conservative incumbent in any of those seats, but he also enjoys the most Republican-leaning electorate. That only raises the stakes higher, and with it the Democratic will to win.

Two recent polls – one for the New York Times and the other for the Los Angeles Times – put Rohrabacher and Rouda neck and neck, with the number of undecided voters apparently shrinking fast. Rouda has been outraising Rohrabacher by a significant margin – he brought in five times as many campaign dollars in August – but both sides have seen massive infusions of support from their national party organizations and from independent groups whose spending is unlimited thanks to the supreme court’s 2010 Citizens United ruling.

The Democratic Congressional Campaign Committee has taken the unprecedented step of setting up a satellite office in the 48th district to act as a regional hub for competitive races across the American west. Much of its focus is right in its backyard, where it says the intensity and spending levels are more akin to a Senate race.

Facebook Twitter Pinterest The number of registered Republicans in California’s 48th congressional district is steadily diminishing. Photograph: Robyn Beck/AFP/Getty Images

Rouda’s strategy is to sell himself as a pragmatist who rejects the politics of division and is more than willing to reach across the political aisle to cut deals and advance legislation in everyone’s interest. “Common sense for common ground,” was the slogan he touted at a recent town hall in Huntington Beach.

“I’m frustrated with both parties putting party first and country second,” he told an eclectic crowd of college students, Democratic party stalwarts, new arrivals in the district, and older, more conservative voters anxious about everything from healthcare to trade wars. “I don’t believe the current representative is doing the job you deserve.”

Those who know Rouda say the campaign posture is an accurate reflection of who he is – a successful businessman who has nothing to prove and has thrown his hat in the ring solely to stop the country sliding in the wrong direction. He represents a strain of centrism that plays poorly to a national Republican audience – as attested by the failed presidential bids of former ambassador Jon Huntsman and Ohio governor John Kasich (whom Rouda backed in 2016) – but has fared rather better on the Democratic ticket in the Trump era.

Rouda’s no-drama, get-the-job-done mantra carries significant echoes of Doug Jones’s successful Senate campaign in Alabama last year, against Republican opponent Roy Moore.

The district does not lack for diehard Trump fans – not to mention a toxic culture of online political warfare that drags even elected officials into the mire – but polling shows that the electorate as a whole supports Dreamers (undocumented immigrants who came to America as young children), believes in protecting the Orange county coastline and has little patience for Rohrabacher’s conspiratorial rejection of climate science.

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As Rouda told the Guardian after the town hall: “I have yet to meet a Republican [here] who wants more offshore drilling. I have yet to meet a Republican who doesn’t think climate change is real.”

Rouda’s argument that Rohrabacher is increasingly out of step with the district has been bolstered several times thanks to the congressman’s own actions. In July, Rohrabacher was tricked on national television by Sacha Baron Cohen into endorsing a bogus proposal to arm preschoolers. His later explanation, that he was referring only to older students, did little to allay consternation in district schools that have staged walkouts and marches in solidarity with the victims of February’s school shooting in Parkland, Florida.

Facebook Twitter Pinterest Two recent polls put Dana Rohrabacher and Harley Rouda neck and neck, with the number of undecided voters apparently shrinking fast. Photograph: Robyn Beck/AFP/Getty Images

Last month, Rohrabacher endorsed a pro-Trump Huntington Beach school board candidate previously slammed for social media posts with racist and antisemitic overtones. This followed hard on reports that last year he and Senator Rand Paul hosted a rightwing activist accused by the Anti-Defamation League of being a Holocaust denier.

Now he is being roasted for a political ad in which he claims to be fighting to keep healthcare coverage for Americans with pre-existing conditions when in fact he voted repeatedly to remove that provision of the Obama-era Affordable Care Act.

It doesn’t help that Rohrabacher is under close scrutiny for his ties to Putin’s Russia and to several key figures in Robert Mueller’s special counsel investigation. One of Rohrabacher’s Republican colleagues, House majority leader Kevin McCarthy, was recorded in 2016 saying he thought Rohrabacher was on Putin’s payroll.

The contrasting energy coming from the two campaigns could not be a starker. While Rouda is energetically barnstorming the district, with the help of a campaign manager and a communications director with deep Washington experience as well as a large team of outreach workers targeting Latinos, Vietnamese Americans and other interest groups, Rohrabacher has been barely visible, apparently banking on the power of incumbency and a defensive posture to see him through.

He rarely grants interviews (a request by the Guardian went unanswered) and has held only a handful of public campaign events. His key campaign aides appear to be his wife Rhonda and her twin sister, Rachelle Carmony, who work out of an upstairs room at Skosh Monahan’s Irish bar and steakhouse in Costa Mesa, sometimes dubbed the Liberty Lounge. A filing with the Federal Election Commission shows that in January the campaign claimed a $844.87 bill from Skosh Monahan’s as a campaign expense for “office utilities”.

And so Rohrabacher has allowed most of the incoming fire to go unanswered: how he is beholden to the gun lobby, the oil industry and big pharma; how he is inaccessible to his constituents; how he has little or no legislative record; how, in the words of Rouda’s campaign manager, Mike McLaughlin, “if you want Dana Rohrabacher to do anything, write him a check”.

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At an online “town hall” he aired on Facebook in August, Rohrabacher sought to attack Rouda in turn by accusing him and Democratic House leader Nancy Pelosi of seeking to “buy” his seat and calling Rouda “a Daddy Warbucks developer without a lick of public service in his background”. It was telling, perhaps, that the town hall featured no apparent interaction with the public and that the Daddy Warbucks reference, from the 1980s film musical Annie, was unlikely to resonate with anyone under 40.

The consensus is that, despite the district’s Republican lean, this is Rouda’s race to lose. Some campaign volunteers worry that the candidate and the party are not working hard enough to turn out working-class Latino voters, who could prove crucial if the election night count gets close, but whose visibility in the campaign could prove a turn-off to Republicans nervous about Rouda being too liberal on immigration.

The disaffected Republican contingent, though, seem to like what they see. “He’s obviously very intelligent. He gets it,” Dan Ardell said after listening to Rouda, skeptically at first, at the Huntington Beach town hall. “What I heard tonight was a Republican talking.” And that, for him, sealed the deal.

