A hip-hop rendition of I Gotta Feeling on electric violin got the crowd jumping. The first glimpse of a 79-year-old democratic socialist got them whistling and whooping. But this time Bernie Sanders was not running for president.

In jacket and open-collar shirt, the Vermont senator had come to an indoor music venue in Cleveland, Ohio to rally for Nina Turner. Not only because she is a close friend, he explained, but to continue his fight for a progressive revolution.

“The real reason I’m here is we desperately need her in the US Congress,” said Sanders, who as chair of the Senate budget committee is enjoying a late-career ascendence. “We have started asking questions that this country has never asked in a very long time and the result of that is we are transforming politics in this country and Washington DC.”

Turner goes head-to-head on Tuesday with Shontel Brown in a primary in Ohio’s 11th congressional district that is being watched closely by Democrats across the nation. An increasingly rancorous campaign has echoed the bitter battle between Sanders and Hillary Clinton in 2016 and suggested party divisions still run deep.

Brown, 46, a council member and county Democratic party chair, is in the moderate evolution-not-revolution lane. Dubbed the “anybody but Nina” candidate, she has been endorsed by Clinton, House majority whip Jim Clyburn – who praised her “substance” at a sparsely attended Black church in Cleveland on Saturday – and the Congressional Black Caucus.

Turner, 53, a former city council member and state senator, is a standard bearer of the left. She was a national surrogate for Sanders’ 2016 campaign, led its spin-off organisation Our Revolution and was national co-chair of Sanders’ 2020 effort. Congresswoman Alexandria Ocasio-Cortez campaigned for her last weekend, underlining Turner’s appeal to young progressives.

The field also includes Jeff Johnson, African American vote coordinator in Ohio for the Clinton campaign in 2016. He said: “It’s not the first congressional race to be nationalised but you would be hard pressed to show me a nastier one. I think this campaign will have reverberations in Washington no matter who wins because of what has been said. There’s some hurt feelings.”

The multimillion-dollar contest offers Joe Biden a sobering warning of potential discord across the country ahead of the next year’s midterm elections. Progressives have announced primary challenges to incumbents in Chicago, Louisville, New York and Nashville and are raising huge sums.

Johnson, 63, said: “The cooperation that came about to get Joe Biden elected is clearly not reflected in what’s going on today. It was a temporary lull in the war when we got to November and this could cause some problems in 2022.”

The seat, which covers most of Cleveland, became vacant when Marcia Fudge resigned to become Biden’s housing secretary. The primary winner will be the overwhelming favourite against weak Republican opposition in November. Both frontrunners are African American women, neutralising gender and race as variables but clarifying differences of ideology and allegiance.

The fight has rekindled hostilities Democrats suppressed for much of the Trump era and has turned acrimonious with negative ads flying. Both Sanders and Turner used Saturday’s rally to condemn an influx of money from oil, drug and insurance companies and other special interest groups.

“Why are they spending all of that money on little old me?” demanded Turner, wearing her trademark thick-framed spectacles. “They like the way things are now. They like it that so few people have so much and so many people have so little … They profit from a system of tax cuts for the rich. They do not want an America as good as its promise and they are investing millions to ensure our voices are silenced.”

The Democratic Majority for Israel political action committee has funded attack ads against Turner – who in May tweeted “Palestinian lives matter” – reminding viewers of her remark last year that voting for Biden instead of Trump was like eating half a bowl of shit instead of a full one.

Meanwhile a Turner commercial focuses on allegations that Brown steered local government contracts to friends and relatives. She is not under any formal investigation but a foreboding voiceover says: “Brown could face criminal charges. And if convicted? Jail time.” It is accompanied by video of a cell door slamming – evocative, critics say, of Trump’s “Lock her up!” chant about Clinton.

Brown hit back with an ad that featured black and white footage of her rival and said: “Turner’s attacks on Shontel Brown? Simply false. Turner has a history of attacking and lying about Democrats.”

The Brown campaign scorns the allegations as “desperate Hail Mary bullshit” inspired by a fringe blog.

Brown told the Guardian: “Baseless. Meritless. Really sad because as a person who has been on the national stage for four-and-a-half years and was boasting about it tremendously, she [Turner] now sees the race slipping away and, rather than running on her record, she wants to sling mud and tell blatant lies.”

She added: “It’s two Black women running for a position of great legacy and influence. It’s disappointing and hurtful.”

‘Who’s been doing the work’

The candidates are eager to resist national framings, pointing to Cleveland’s history and local dynamics. This was once the home of oil baron John D Rockefeller, the Jeff Bezos of his day, and the great African American Olympian Jesse Owens. In 1967 it elected the first Black mayor of a major US city; its public schools were desegregated in 1976. It is still among the poorest and most racially divided major US cities.

Brown’s campaign office is in the charming middle-class surroundings of Shaker Square, the second-oldest planned shopping centre in America. Asked if the primary is effectively a rerun of Clinton v Sanders, she said: “Given the fact that Hillary won the district 68 to 32, I’ll take that narrative if that’s again going to be the outcome.

“But that’s the national narrative. It fits into an easy headline but it really comes down to who’s been doing the work. If all politics is local then I am as local as it gets. I’ve been here my whole life – never left – I’ve been doing the work of a legislator for nine consecutive years, delivering for my constituents and other elected officials. Long before we started getting the national attention and national support, I earned the support of over 100 local elected officials.”

Brown describes herself as “very much aligned” with Biden, able to support his ambition for the federal government to deliver resources and infrastructure. She said: “On the local level, people now who’s been doing the work, who’s been delivering for them, and that is really the bottom line. Again, I guess that’s not sexy, but that’s the real substance here that has afforded me what some would describe as a surge.”

Turner, by contrast, would swell the ranks of “the squad” in the House and be a potential thorn in the side of the speaker, Nancy Pelosi. But like Sanders, she is striking a conciliatory and pragmatic tone and did not mention Biden or Brown at the rally, instead emphasising priorities such as an $15-an-hour minimum wage, Medicare for all and the Green New Deal.

Stephanie Howse, an Ohio house member who endorsed Turner, said: “The average person in our community, they don’t care about no Hillary Clinton and Bernie stuff. Go to a gas station, go to a grocery store, talk to to our people. They want somebody that’s going to centre them. It makes for a good headline to talk about the Hillary-Bernie. That ain’t how we live our lives. People are trying to figure out how are they going to get through the day. We are coming upon the moratorium ending on evictions.

“‘How am I going to be able to stay in my house? How am I going to pay this running back payment that I owe? How am I going to be sure in a global pandemic that my baby is going to be safe going to school?’ Those are the things that people care about and we have to have someone that goes to Congress that thinks about that, fights for that every single day, and we know that Nina will do that. That’s why the people are with her and she will become our next congresswoman come Tuesday.”

‘We ought not to be fanning the flames’

Clyburn, the highest-ranking African American in the House, arguably played a bigger role in Biden’s election than anyone else when his endorsement in South Carolina helped the ailing candidate turn the Democratic primary around. The kingmaker is hoping to work the same magic and become queenmaker for Brown, whom he has known for years.

“I think she’s a great person to work with and I do feel strongly that we have to stop this sloganeering for headlines when we’re in such a precarious place in this country,” Clyburn said by phone.

“We just have to wake up to the fact that there’s a strong rightward shift taking place in this country and we’d better arrest that. We ought not to be fanning the flames but doing what is necessary to gain as many friends as we possibly can and I think you’re more successful with honey than vinegar.”

Simmering tensions among Democrats in Washington flared again this week when Ocasio-Cortez and other progressives lambasted the Arizona senator Kyrsten Sinema for refusing to support a $3.5tn bill that would invest in childcare and climate.

But Clyburn insisted: “The party is united, and united does not mean unanimous. I differentiate between those two.”

But that unity felt fragile at Saturday’s Turner rally, which attendee Ryan Ashley, a car workers union employee, found reminiscent of the 2016 primary in which Sanders pushed Clinton hard.

“It kind of feels like that with a grassroots campaign against a corporate-backed Democrat,” the 21-year-old said. “I believe progressives are being heard more. In 2015-16, Bernie’s ideas were radical. A lot of those ideas are getting implemented now in states and towns. They’re not so radical any more.”

The author and pollster John Zogby sees Ohio’s 11th congressional district as indicative of a wider struggle within the Democratic party.

“In the communities, in the bigger cities throughout the country, this is the battle that is being waged,” he said. “It’s very much a local from-the-bottom-up thing. It’s amazing how half the parties, especially in the cities, belong to Bernie. There are local activists out there that are winning local races.”