Can middle-class candidate Daniel Biss defeat millionaires in Illinois?

In an Illinois governor race that includes a couple millionaires and a billionaire, Daniel Biss likes to tell people he's given his campaign just $25 - and then his wife decided to one-up him and donate $50.

"We're pretty well maxed out, but we'll see what we can do going forward," the Democratic state senator from Evanston said at a recent event, drawing laughs from some and serious nods from others.

Biss, a former math professor who reported income of less than $35,000 last year, has gained support in recent weeks campaigning as a progressive who's something the other top candidates are not: part of the middle class.

In TV ads filmed in his family's modest home, he talks about sending his kids to public school and living on a budget.

In another ad, he links wealthy Democratic rivals J.B. Pritzker and Chris Kennedy to two Republicans, Illinois Gov. Bruce Rauner and President Donald Trump, calling them all "rich guys" who've avoided taxes.

Several recent polls have shown him surpassing Kennedy, the son of the late Sen. Robert Kennedy, and gaining ground on Pritzker. The billionaire heir to the Hyatt hotel fortune and perceived front-runner has the support of many Democratic leaders in the March 20 primary - partly because he has the money to take on Rauner.

Other candidates across the U.S. also are making wealth - or their lack of it - a campaign theme.

In Florida, Democratic Tallahassee Mayor Andrew Gillum talks about growing up poor and how he can't write his campaign for governor a big check, unlike his wealthier rivals. Wisconsin Democrat Mike McCabe, a former director of a government watchdog group who's long complained about the influence of money in politics, wears jeans to all his gubernatorial campaign functions, and is the founder of Blue Jean Nation, a group he says is dedicated to electing "regular people."

But none of them has so far faced a financial disadvantage as large as the one confronting Biss, who has raised about $4.8 million, mostly through small donations. That includes about $1 million he carried over from prior races.

Pritzker has already sunk close to $50 million into his campaign - a number Biss notes is more than Trump spent in the GOP presidential primary. Rauner, who's seeking his second full term, has raised more than $75 million, most from his own bank account. If Pritzker and Rauner face off in the November general election, the contest is expected to be the most expensive governor's race in U.S. history.

Biss calls the race "a referendum on money in politics."

"Do we need in the era of Trump and Rauner to just pick another inexperienced billionaire?" he asks.

First elected to the Legislature in 2010, the graduate of Harvard and MIT became known as a numbers guy who tackled issues such as Illinois' hugely underfunded pension system. He still has a wonky streak, including publishing a series of videos where he does such things as juggle flaming objects while explaining the pension and state budget mess.

His bid for governor was met early on by "a thunderous chorus of yawns," Biss says. But he has picked up support from several colleagues in the General Assembly and the endorsement of progressive groups, including those who supported Vermont Sen. Bernie Sanders' presidential campaign.

He also has drawn the attention of Pritzker, who's attacking Biss for leading the charge on a 2013 public-pension overhaul, among other issues, with a series of ads that question his progressive credentials.

The pension measure aimed to reduce Illinois' multibillion-dollar unfunded liability, in part by slashing benefits for hundreds of thousands of state workers and retirees. The plan, which the Illinois Supreme Court later found unconstitutional, infuriated labor unions and others in the Democratic Party's base.

Biss now says he believes pension benefits should not be cut. Asked about the change during an interview with Crain's, Biss said it was "a long learning process for me, and I wish I'd learned that lesson differently." The Pritzker campaign pounced.

"Biss can try and ramble and deflect now, but this is someone who needed the Supreme Court to step in before he 'learned his lesson' that working families deserve the pensions that were promised to them," Pritzker spokeswoman Galia Slayen said.

Biss noted Pritzker and his wife gave $20,000 to a political committee created to fund lawmakers who were willing to take on unions. He said Pritzker is worried because of the shift happening in the race, including the Pritzker campaign's own poll numbers showing Biss in second place - though that polling also showed Pritzker with a healthy lead.

Pritzker also has been working to repair damage from newly released FBI wiretaps recorded a decade ago for the investigation of ex-Gov. Rod Blagojevich, who is serving a 14-year prison sentence for corruption. Pritzker is heard on the tapes saying racially insensitive comments while talking with Blagojevich about appointing someone to a vacant Senate seat.

Rabia Amin, a 19-year-old political science major at Elmhurst College, said she plans to vote for Biss. It was his ads set in a home that looked much like her own that sealed her decision.

"I thought, 'Oh my god. He's a normal human being,'" she said. "That's the thing I've been getting from him. He understands our problems, because I feel like he's gone through them, and I really like that."

Three other candidates are seeking the Democratic nomination: educator Bob Daiber, activist Tio Hardiman and physician Robert Marshall. Rauner faces state Rep. Jeanne Ives in the GOP primary.

• Associated Press reporters Brendan Farrington in Tallahassee, Florida, and Todd Richmond in Madison, Wisconsin, contributed.