The fact that Donald Trump was here at all said more about a looming electoral disaster facing his Republican party next month than anything contained in his dark and discursive 98-minute stump speech.

On Monday, amid raucous chants of “USA! USA!”, the president held his first campaign rally in Kansas for eight years. No Democrat has won a US Senate seat in this ruby-red state since 1932, the year Herbert Hoover was president, Amelia Earhart was the first woman to fly solo across the Atlantic and the Nazis became the biggest party in the German Reichstag.

Since then Republicans in the state have built one of the longest winning streaks in Senate history, but such is the collapse in public esteem of the president that the midterms on 3 November could be the night that a blue wave engulfs the heart of Trump country.

“You’re really sort of – I hate to say it – you’re sort of tending toward the purple,” the president told about 5,000 supporters in a multipurpose arena outside Wichita, acknowledging that Kansas already has a Democratic governor in Laura Kelly. “That’s why I have to be sure that we get this guy.”

The “guy” concerned was Roger Marshall, a first-term Republican senator facing an unexpectedly strong challenge from Democrat Adam Hamilton, a Methodist megachurch pastor. Opinion polls show them running neck and neck. In the third quarter, Hamilton reportedly raised $11m while Marshall managed just $800,000.

Marshall, 66, is an obstetrician-gynaecologist and ex-congressman who has proved a staunch Trump ally, including by embracing his debunked claim that the 2020 presidential election was stolen. Hamilton, 62, founded the 24,000-member Church of the Resurrection, the biggest United Methodist congregation in the country. He opposes Trump’s tariff agenda and what he calls the president’s “erratic leadership”.

Despite Hamilton’s background as a pastor and former Republican, Marshall insisted on Monday that Hamilton was “too woke for Kansas”. Accompanied by Chuck Berry’s Johnny B Goode as he walked on stage, Marshall said: “This is a guy that participates in protests against police. He supports drag shows. He tells us to apologise for the colour of our skin. And in a state with more cattle than people, he tells you to stop eating beef.” The crowd jeered each time.

Trump, 80, is barnstorming the country in what some have called a “desperation tour” aimed at rescuing Republicans from the hole he has dug for them. Critics suggest he might actually be making life harder by nationalising races that candidates would prefer to keep focused on local issues.

By imposing himself in Kansas, at a rally that was disrupted by several protesters, Trump underlined the election as a referendum on his presidency, with the potential to cost Republicans control of both the Senate and House of Representatives just two years after they swept into power.

Farmers in Kansas, a heavily agricultural state, have been hit hard by the consequences of the Iran war: a gallon of diesel costs nearly $6. The president upset cattle ranchers with a plan to reduce import tariffs to lower the price of beef and with aggressive immigration raids that prompted some agricultural workers to stay at home. On Monday Trump announced a new program to provide farmers with $8bn in support to offset diesel costs during the harvest season.

The election will test whether the old playbooks that fuelled his presidential campaigns – hurling insults, stirring bigotry and telling lies – can still work among an electorate weary of the cost of living, foreign wars and government corruption.

Trump launched a tirade against Hamilton, dismissing him as a “radical left lunatic” and a “phoney who’s pretending to be a moderate”. Trump claimed the Democrat supports flooding Kansas with refugees who “go around killing people”, that he used church money to fund “transgender crap”, that he “openly mocks Jesus” and that he believes America is systemically racist.

“He wants you to repent for being born white,” Trump said.

The president also sought to weaponise the recent upheaval in France, pushing the baseless nativist claim that the violence is being led by immigrants. “We’re not going to let that happen to this country,” he said. “When you see burning steeples and raging fires in France, just remember that is what the radical Dumocrats want to ​do to America.”

Trump unleashed bitter attacks on three Muslim politicians: Abdul El-Sayed, Ilhan Omar and Rashida Tlaib. When Tlaib’s name was mentioned, members of the crowd yelled: “Deport her!” Trump falsely claimed that both El-Sayed and his sister are members of the Muslim Brotherhood, an Islamist opposition group in Egypt. He mockingly warned that, should El-Sayed be elected and sit on the Senate intelligence committee, he would leak information to the enemy.

Supporters roared their approved, thrilled by what they saw as Trump’s transgressive daring. The president, who won Kansas by 16 percentage points against Democrat Kamala Harris in 2024, showed he can still draw a crowd in one of the most surprising battleground states in the country.

Earlier, in warm sunshine, a long line of people snaked through fields outside the 5,000-seat multi-purpose arena in Park City, Kansas. There were sights that have become familiar over more than a decade: giant Trump flags, tables full of “Make America great again” caps, spangly “DJT” and “Trump the golden age” jackets, “Alligator Alcatraz” merchandise, “We are all Charlie Kirk now” sweaters and T-shirts that said “Stand for the flag, kneel for the cross”.

One woman wore a sweater that said: “0% liberal.” One man wore a T-shirt that declared: “I love Trump because he pisses off all the people I can’t stand.”

For these supporters, Trump rallies are galvanising and still the best way to get out the Republican vote. Cybersecurity worker Justin Nelsen, 44, said: “It fires us up, it gets us all excited for the cause and allows us to put out there what we want here as the state of Kansas. That’s why I’m here.”

Attendees were aware of the danger posed by Hamilton. Brittany Jones, a 33-year-old lawyer wearing a Stars and Stripes sweater, said: “If you know Adam Hamilton at all you know that he’s a problem and a chameleon and good at saying what he thinks people want to hear, even if he doesn’t believe it. He has shown himself to be not only a turncoat to things that matter to Christians, he has wholly given himself to the local agenda. Even though he claims to be a moderate, there’s nothing moderate about him.”

A Democratic victory here would represent a political earthquake, Jones acknowledged. “It’s seismic. It would be sad for most Kansans when they realise what happened, and some people just aren’t thinking through the consequences, but he has a built-in audience of people who are highly motivated.”

Jones, who had her friend’s three-month-old baby, Hannah, tucked under one arm, said she mostly welcomed Trump’s second term. “Overall I care about the social issues and he’s done a lot to protect girls’ sports, he’s done a lot to protect kids from being put through harmful gender transition procedures. Those things matter to me, they matter to the future of girls all across Kansas and America, and so I’m excited about those things.”

Construction worker Thad Snider, 42, who attended wearing a red “Make America Great Again” T-shirt alongside his mother, said he was not overly worried about the Senate seat falling to the Democrats.

“I don’t think Adam’s as strong a candidate as what the media is trying to sell him as,” he said, pointing to Hamilton’s past political donations to Democrats including Hillary Clinton. “I don’t think it’s going to happen but, if it did happen, it would be very shocking.”

Snider argues that voters faced a stark choice between political parties, describing the Republicans as the “least bad” option because “at least they’re not socialists or communists”. He added that he disagreed with foreign wars and wished Trump had done more on election integrity, but remained loyal to the president. “Any time you turn around a battleship, it takes time.”

That sentiment was echoed by Darrell Claphan, 72, a retired sales worker, who said of Trump: “He’s doing fantastic. He’ll go down in history being the number one president at what he’s done for the country in my lifetime.”

Claphan dismissed opinion polls showing a close race, stating: “Polls have been wrong ever since I’ve been alive.”

Asked how he would react to a Democratic Senate victory in Kansas, Claphan said: “I’d be shocked. But I don’t think it’s going to happen.”