Early this week, an underdog candidate savaged his opponent for “using the language of Donald Trump” and insisted “civility is on the ballot” in the looming midterm elections. The speaker was not a Democrat.

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It was Peter Roskam, a six-term Republican from a gerrymandered district who nonetheless finds himself clinging onto his seat, and in doing so attempting to cast his progressive opponent as the Trumpian one in the race.

In suburban districts across the US, politics as usual has been turned on its head. Nowhere is this more so than in two districts outside Chicago that were long represented by Republican stalwarts such as Henry Hyde and Dennis Hastert. Among the prosperous and well-educated suburbanites who once made up its base, the GOP is facing rejection.

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Roskam has long been aware of the threat. A former member of House Republican leadership who helped write the 2017 tax cut bill, he represents Illinois’ sixth district. It is one of the wealthiest districts in the country. In 2016, Hillary Clinton won it by seven points. In 2012, Mitt Romney won it by even more.

From the sixth, the threat of a blue wave of Democratic victories has rolled out to the exurban expanses of the 14th district, which is represented by Randy Hultgren. Out where cornfields are being gobbled up by subdivisions and Starbucks, he is in a tight race on once-red turf that Clinton narrowly lost.

I don’t see how the numbers add up for the Democrats to win if they don’t win probably both the sixth and the 14th Randy Hultgren

As the Democrats look to take back the House, such seats are vital battlegrounds. Hultgren told the Guardian the two Illinois races “likely could be determinative of Congress. I think I don’t see how the numbers add up for the Democrats to win if they don’t win probably both the sixth and the 14th.”

Roskam, who has the moderate mien of a somewhat tweedy stockbroker, has staked his campaign entirely on discrediting his opponent, businessman Sean Casten, with swing voters. The Democrat is a first-time candidate with a deep flaw: he tends to say precisely what’s on his mind, without care for the consequences.

Sometimes, this is impressive. At a suburban train station, in the darkness before dawn, he was able to address in elaborate detail a commuter’s concern about her property taxes. Sometimes, it is unusual. Addressing a room of roughly 50 voters, Casten said those who settled Jamestown, the first permanent English-speaking settlement in North America, “were horrible people” who “did not assimilate, they were vectors of disease, they didn’t learn the language and they died”.

Casten has found trouble, on which Roskam has naturally dwelled. After national Republicans backed Roy Moore in the Alabama special election last year, Casten called the GOP “the pedophile party”. He has also called Republican donors “morons” and, most notoriously, named sex columnist Dan Savage as a personal hero.

At a recent event with Marco Rubio, Roskam showed reporters a web ad that focused on Casten’s praise for Savage and the columnist’s attempts to redefine former Republican presidential candidate Rick Santorum’s name in vulgar sexual terms. Casten, Roskam insisted to the Guardian, was a candidate who “embraced the attributes of Donald Trump that this district doesn’t like: the name-calling, the tweeting and some of the vitriol”.

In contrast, he said, the district liked Trump’s accomplishments: “Tax policy, regulatory policy, rebuilding the military, moving the US embassy to Jerusalem and getting out of the Iran deal.”

‘The No 1 issue’

Roskam did not tout perhaps the most notable piece of legislation that passed the House in the past Congress, the American Health Care Act (AHCA).

In the 14th district, that bill has become the driving issue. The Democrat seeking to unseat Hultgren is Lauren Underwood, a 31-year-old African American nurse who has focused on protections for those with pre-existing conditions – such as herself. Underwood has targeted Hultgren’s support for the AHCA and what she called his decision to break a promise to protect those with pre-existing conditions.

If every voter in the 14th thinks, ‘Randy Hultgren OK, oh Lauren Underwood, she’s the nurse,' We’ve done our job Lauren Underwood

In an interview with the Guardian, she dismissed suggestions she was a “single-issue candidate”.

“Healthcare is the No 1 issue in this election for across the board,” she said. “Not the No 1 for Democrats, not the No 1 for men. It’s No 1 across the board. I’m a nurse. And if every voter in the 14th walks into their polling place thinking, ‘Randy Hultgren OK, oh Lauren Underwood, she’s the nurse,’ we’ve done our job.”

Hultgren, a soft-spoken four-term incumbent, said: “People can kind of say anything. It’s, you know, free speech still has some limitations but not in politics. I mean you really can pretty much say anything. I just believe this is not true.”

While healthcare is “an important issue”, he said, the biggest issue he had seen while going door to door was concern about state issues.

Underwood’s campaign has certainly tapped into voter energy fueled by opposition to Trump. Martha Paschke, a 39-year-old volunteer helping female activists reach out to female voters, cited “the political atmosphere after the 2016 election” as a reason for her involvement. Although she had volunteered in passing before, she said, her desire was charged by a sense of guilt that she did not do enough for Clinton.

“Now we are looking at this midterm and have a sense of guilt that maybe if we’d helped Hillary’s campaign, maybe we would have reached that one extra voter, maybe we could have made enough of a difference that we wouldn’t be living in times that often feel cataclysmic,” she said.

Facebook Twitter Pinterest Randy Hultgren, seen on Capitol Hill. Photograph: Bill Clark/CQ-Roll Call,Inc.

At a rally Underwood held with former vice-president Joe Biden, Kate Nelsen, a nurse from St Charles, said that in her neighborhood, “the older generation is more of the Republican side while the younger families moving in are more Democrat”. Nelsen also noted that many Republicans, including her father, had broken from the party over Trump.

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The question is, how many.

‘Run on your voting record’

Casten was not worried about Roskam comparing him to Trump. In typical fashion, he called the analogy “garbage” and accused Roskam of engaging in “gaslighting”. He thought Trump had forced his district to face a political reckoning.

“Trump made manifest how far rightward the GOP has managed to go,” he said. “Now you actually have to run on your voting record as opposed to how you characterized yourself with voters.”

This resonated with at least one voter. After a Casten town hall in Cary, a former Republican from Wheaton, Steve Anderson, told the Guardian he was repelled by Trump.

A former Roskam voter, he said: “If you are going to stand with Trump, you are against the values I hold.” He dismissed Roskam’s mild criticism of the president and compared the Republican to Neville Chamberlain – for what he saw as appeasement.

Nonetheless, Roskam was still optimistic.

“I know what it’s like to be in an environment that’s challenging,” he said. “I go back to my first race, which was tough.”

That was a contest against Tammy Duckworth, now a US senator.

“George W Bush was not popular,” Roskam continued. “The war in Iraq was not popular. Tammy Duckworth, based on her service story, was phenomenal.”

A question lingered: was the Bush of 2006, damaged by war and Hurricane Katrina, less of an anchor on Republicans than Trump is today?