LINCOLN, Ill. — Darren Bailey, the front-runner in the Republican primary for governor of Illinois, was finishing his stump speech last week at a senior center in this Central Illinois town when a voice called out: “Can we pray for you?”
Mr. Bailey readily agreed. The speaker, a youth mentor from Lincoln named Kathy Schmidt, placed her right hand on his left shoulder while he closed his eyes and held out his hands, palms open.
“More than anything,” she prayed, “I ask for that, in this election, you raise up the righteous and strike down the wicked.”
The wicked, in this case, are the Chicago-based moderates aiming to maintain control over the Illinois Republican Party. And the righteous is Mr. Bailey, a far-right state senator who is unlike any nominee the party has put forward for governor in living memory.
A 56-year-old farmer whose Southern Illinois home is closer to Nashville than to Chicago, he wears his hair in a crew cut, speaks with a thick drawl and does not sand down his conservative credentials, as so many past leading G.O.P. candidates have done to try to appeal to suburbanites in this overwhelmingly Democratic state. On Saturday, former President Donald J. Trump endorsed Mr. Bailey at a rally near Quincy, Ill.
Mr. Bailey has upended carefully laid $50 million plans by Illinois Republican leaders to nominate Mayor Richard C. Irvin of Aurora, a moderate suburbanite with an inspiring personal story who they believed could win back the governor’s mansion in Springfield in what is widely forecast to be a winning year for Republicans.
Mr. Bailey has been aided by an unprecedented intervention from Mr. Pritzker and the Pritzker-funded Democratic Governors Association, which have spent nearly $35 million combined attacking Mr. Irvin while trying to lift Mr. Bailey. No candidate for any office is believed to have ever spent more to meddle in another party’s primary.
The Illinois governor’s race is now on track to become the most expensive campaign for a nonpresidential office in American history.
Public and private polling ahead of Tuesday’s primary shows Mr. Bailey with a lead of 15 percentage points over Mr. Irvin and four other candidates. His strength signals the broader shift in Republican politics across the country, away from urban power brokers and toward a rural base that demands fealty to a far-right agenda aligned with Mr. Trump.
For Mr. Bailey, the proposal to excise Chicago, which he called “a hellhole” during a televised debate last month, encapsulates the grievances long felt across rural Central and Southern Illinois — places culturally far afield and long resentful of the politically dominant big city.
“The rest of the 90 percent of the land mass is not real happy about how 10 percent of the land mass is directing things,” Mr. Bailey said in an interview aboard his campaign bus outside a bar in Green Valley, a village of 700 people south of Peoria. “A large amount of people outside of that 10 percent don’t have a voice, and that’s a problem.”
That pitch has resonated with the conservative voters flocking to Mr. Bailey, who seemed to compare Mr. Irvin to Satan during a Facebook Live monologue in February.
“Everything that we pay and do supports Chicago,” said Pam Page, a security analyst at State Farm Insurance from McLean, Ill., who came to see Mr. Bailey in Lincoln. “Downstate just never seems to get any of the perks or any of the kickbacks.”
The onslaught of Democratic television advertising attacking Mr. Irvin and trying to elevate Mr. Bailey has frustrated the Aurora mayor, whose campaign was conceived of and funded by the same team of Republicans who helped elect social moderates like Mark Kirk to the Senate in 2010 and Bruce Rauner as governor in 2014. Their recipe: In strong Republican years, find moderate candidates who can win over voters in Chicago’s suburbs — and spend a ton of money.
Mr. Irvin, 52, fit their bill. Born to a teenage single mother in Aurora, he is an Army veteran of the first Gulf War who served as a local prosecutor before becoming the first Black mayor of the city, the second most populous in Illinois.
Kenneth Griffin, the Chicago billionaire hedge fund founder who is the chief benefactor for Illinois Republicans, gave $50 million to Mr. Irvin for the primary alone and pledged to spend more for him in the general election. Mr. Griffin, the state’s richest man, will not support any other Republican in the race against Mr. Pritzker, according to his spokesman, Zia Ahmed. Mr. Griffin announced last week that his hedge fund and trading firm would relocate to Miami.
While Mr. Irvin, a longtime Republican who has nevertheless voted in a series of recent Democratic primaries in Illinois, expected an expensive dogfight in the general election, he is frustrated by the primary season intervention from Mr. Pritzker, a billionaire who is America’s richest elected official.
“This has never happened in the history of our nation that a Democrat would spend this much money stopping one individual from becoming the nominee of the Republican Party,” Mr. Irvin said in an interview after touring a manufacturing plant in Wauconda, a well-to-do suburb north of Chicago. “There are six Republican primary opponents — six of them. But when you turn on the television, all you see is me.”
Mr. Griffin said that “J.B. Pritzker is terrified of facing Richard Irvin in the general election.”
He added, “He and his cronies at the D.G.A. have shamelessly spent tens of millions of dollars meddling in the Republican primary in an effort to fool Republican voters.”
Mr. Pritzker said that ads emphasizing Mr. Bailey’s conservative credentials had the same message he plans to use in the general election. He said he was not afraid of running against Mr. Irvin or of the millions Mr. Griffin would spend on his campaign.
“It’s a mess over there,” Mr. Pritzker said in an interview on Friday. “They’re all anti-choice. Literally, you can go down the list of things that I think really matter to people across the state. And, you know, they’re all terrible. So I’ll take any one of them and I’ll beat them.”
The primary race alone has drawn $100 million in TV advertising. Mr. Pritzker has spent more money on TV ads than anyone else running for any office in the country this year. Mr. Irvin ranks second, according to AdImpact, a media tracking firm.
Far behind them is Mr. Bailey, whose primary financial benefactor is Richard Uihlein, the billionaire megadonor of far-right Republican candidates, who has donated $9 million of the $11.6 million Mr. Bailey has raised and sent another $8 million to a political action committee that has attacked Mr. Irvin as insufficiently conservative.
Presidential politics for both parties loom over the primary.
Mr. Irvin won’t say whom he voted for in the 2016 and 2020 presidential elections and, in the interview, declined to say if he would support Mr. Trump if he ran for president in 2024. He called President Biden “the legitimate president” and said former Vice President Mike Pence had performed his constitutional duty on Jan. 6, 2021.
As the primary draws near, establishment Republicans across the state are fretting about the prospect of Mr. Bailey dragging down the entire G.O.P. ticket in November.
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Representative Darin LaHood predicted an “overwhelming” Bailey primary victory in his Central Illinois district, but warned that he would be toxic for general-election voters.
“Bailey is not going to play in the suburbs,” said Mr. LaHood, who has not endorsed a primary candidate. “He’s got a Southern drawl, a Southern accent. I mean, he should be running in Missouri, not in suburban Chicago.”
Former Gov. Jim Edgar, the only Illinois governor from outside the Chicago area since World War II, said Mr. Bailey’s rise showed that party leaders “don’t have the grasp or the control of their constituents like they did back in the ’80s and the ’90s.”
Mr. Bailey’s supporters say the real fight is for the soul of the Republican Party. To them, winning the primary and seizing control of the state party is just as important, if not more so, than triumphing in the general election.
Running for attorney general on a slate with Mr. Bailey is Thomas DeVore, his lawyer in the pandemic lawsuits against Mr. Pritzker. On the campaign trail, he wears untucked golf shirts that reveal his forearm tattoos — “Freedom” on his right arm, “Liberty” on his left.
“Whether or not Darren and I win the general election, if we can at least get control within our own party, I think long term we have an opportunity to be successful,” Mr. DeVore said at their stop in Green Valley.
And David Smith, the executive director of the Illinois Family Institute, an anti-abortion organization whose political arm endorsed Mr. Bailey, said the G.O.P. race was about excising the party’s moderate elements.
“This primary,” he said, “has got to purge the Republican Party of those who are self-serving snollygosters.”
Catie Edmondson contributed reporting from Mendon, Ill.