JOE DONNELLY is almost indistinguishable from the voters he is mingling with in Doug Burnworth’s barn. A burly figure, in denim jeans and a yellow shirt bearing the legend “Indiana Pork”, the Democratic senator from Indiana looks like a prosperous farmer. He also knows his onions—or rather, his corn and soyabeans, the main crops in Noble County, northern Indiana.

For the crowd of farmers gathered to hear him, Mr Donnelly has news on the provisions for water management and crop insurance in the forthcoming Senate agriculture bill, which he helped write. He commiserates over the effects of President Donald Trump’s budding trade war, including a 20% hit to soyabean prices. But he does not blame Mr Trump, for whom most of the farmers—and over 70% of folk in Noble County—voted. His attitude towards the president is one of amiable concern, which he expresses while recounting their slightest interaction in minute detail. (“He said, ‘Hey Joe, can you come over?” “I said, sure!”) Not once do the words “Democrats” or “Republicans” pass his lips.

It is a performance redolent of a former time in American politics, when partisan divisions were subservient to local leaders and issues. It is wholly at odds with talk of a progressive wave and a national verdict on Mr Trump in the mid-terms, which Mr Donnelly is campaigning for. Yet if the Democrats take either congressional chamber, especially the Senate, it will be thanks to gritty heartland moderates like him, battling for re-election in states such as Missouri, Montana, North Dakota and West Virginia, as well as Indiana. These are places where Mr Trump won big and is still popular; and where voters are liable to consider social democracy as something America defeated in the cold war.

That means Democrats like Mr Donnelly need to steer clear of the divisive national issues—including Mr Trump himself—their left-wing colleagues obsess over. A mastery of retail politics and local issues is their principal means. Paradoxically, this ensures their races are at once the most nationally significant and the most grounded in local politics. “Anyone need a passport or something, let us know,” says Mr Donnelly, before engaging a group of farmers’ wives on the quandary of freezing v canning.

Alongside Heidi Heitkamp of North Dakota, he is probably the most endangered Democrat up for re-election. Indiana, which Mr Trump won by 19 points, is the most conservative state in the Midwest. It has backed the Republican presidential candidate in every election since 1964 bar one, when it voted for Barack Obama in 2008. As a big steel producer, it also has a lot of people who like Mr Trump’s tariffs. Its logistics and manufacturing industries, situated at the crossroads of America, are booming. Mr Donnelly’s Republican challenger, Mike Braun, the boss of a car-parts firm and a former member of the statehouse, naturally claims that the senator is an enemy of this progress. He cites his opposition to last year’s plutocratic tax cut.

Yet Mr Donnelly, who votes with Mr Trump more often than not, is no out-of-touch liberal. He is rated one of the most socially conservative Democratic senators, rarely speaks to the national media, and focuses on issues, such as veterans’ affairs, that Trump voters like. “The natural Trump coalition—farmers, firemen, policemen, veterans, small businessmen—has always been my coalition,” he says. “They voted for me before and I’m very hopeful they’ll do it again.” Polls say the race is too close to call.

That Mr Donnelly is even competitive is remarkable. It also illustrates why the ideological purity demanded by some progressive Democrats is insane. Democrats cannot win legislative power without winning in some conservative states. And to do so they need, more than populist or ingenious economic policies, candidates that conservatives voters can trust. Mr Donnelly, a rare anti-abortion Democrat, gets a hearing from Hoosiers because he is on their cultural wavelength. The fact that Joe Biden, another hardscrabble moderate, is the only member of Mr Donnelly’s party that he has allowed to campaign with him suggests how few Democrats cross that bar. “I’ve always kind of ridden around in my own truck,” the senator says delicately.

Yet moderates like Mr Donnelly are more than an awkward necessity to their party. Having to overcome their constituents’ partisan bias means they understand and represent them to a rare degree. That is a lesson for complacent partisans of all stripes. It is no coincidence contempt for politicians and the prevalence of uncompetitive congressional races are rising in tandem.

The ideological diversity conservative Democrats bring to their party is also good in itself. Mitigating groupthink helps produce better policy. On financial regulation, health-care policy and the like, moderates have consistently offered pragmatism and a check on the righteousness of their progressive colleagues.

Ideological conformity, and the damage it does, is even more apparent among Republicans, whose moderate wing is even more diminished. For all their strengths, Mr Donnelly and his counterpart in Missouri, Claire McCaskill, probably owe their jobs to it. Her Republican rival in 2012 imploded by arguing, to explain his opposition to abortion, that women who had suffered a “legitimate rape” rarely conceived. Mr Donnelly’s opponent argued that conceptions following rape were “something that God intended to happen”.

Reaping what you sow

In the current contest, Mr Trump’s tariffs could be another act of Republican self-sabotage. Even the most Trump-loving farmers in Mr Burnworth’s barn seemed mildly shocked by them. Others, noting the excellence of this year’s soyabean crop, were openly livid. The $12bn in compensation Mr Trump has promised was additionally enraging, some said. It was disrespectful. “This guy is trying to treat American agriculture like Stormy Daniels,” said Mel Egolf, who farms 1,900 acres and has voted Republican all his life. “He’s saying take my money and keep quiet.”