When U.S. Sen. Dick Durbin announced last April he would not seek a sixth term, he created the state’s first open U.S. Senate seat in a generation and kicked off a tumultuous campaign that has unfolded amid the turbulence of President Donald Trump’s second term.

Since then, Illinois Democrats have battled through a primary shaped by Trump’s aggressive and sometimes deadly federal immigration enforcement, threats to strip federal funding from Illinois and other states that have opposed him and, more recently, a war with Iran.

On Tuesday, voters will choose the nominees to succeed Illinois’ senior senator — the chamber’s No. 2 Democrat — ending a crowded and expensive scramble among 10 Democrats and six Republicans seeking the first open Senate seat in Illinois in 16 years.

On the Democratic side, the contest has narrowed to three leading contenders — U.S. Reps. Raja Krishnamoorthi of Schaumburg and Robin Kelly of Lynwood and Lt. Gov. Juliana Stratton — in a race that has become noteworthy for how modern-day federal campaigns are financed by inside and outside influences.

The outcome could also serve as a measure of Democratic Gov. JB Pritzker’s reach as he seeks a third term and ponders a potential 2028 presidential bid. The state’s Democratic voters will gauge the extent of his political power and personal fortune through his support for Stratton, his two-term running mate.

The top tier of the Democratic field formed quickly after Durbin’s April 23 announcement. Stratton entered the race the next day, Kelly followed on May 6, and Krishnamoorthi joined a day later.

The contest that followed featured one key recurring theme — chiefly a vow by each candidate that they were the strongest Democrat to confront Trump and his administration. But just as front-facing was a running battle between Stratton and Krishnamoorthi, alleging that the other was being funded by Trump donors and federal immigration contractors.

That fight, waged in debates and in millions of dollars in television advertising from their campaigns and independent outside interests, has sidetracked the contest by plunging voters into the wormhole of how federal campaigns are financed rather than seeing the candidates elaborate on their issue differences.

Candidates do disagree on issues

Those differences do exist. Stratton has sought to present herself as a progressive outsider to Washington, contrasting with two veteran members of Congress who argue their experience gives them a clearer path to passing legislation in a polarized Capitol.

Stratton alone has called for the abolishment of the federal Immigration and Customs Enforcement agency. Krishnamoorthi has said “Trump’s ICE” should be abolished, along with reforming immigration enforcement. Kelly, who pushed for the impeachment of now-former Homeland Security Secretary Kristi Noem, wants to see the entire Homeland Security agency restructured.

Stratton has also pushed for an immediate $25-per-hour federal minimum wage to replace the current $7.25 wage set in 2009. Both Krishnamoorthi and Kelly argue Stratton’s approach could harm small businesses and entry-level jobs and say a gradual increase to $17 an hour is more politically achievable.

Stratton and Kelly have vowed not to vote to confirm any new Trump appointees to his Cabinet or to the U.S. Supreme Court. Krishnamoorthi has said he would block “radical” judicial appointees to the Illinois federal bench and seek intensive vetting of Supreme Court nominees. He also is the only one advocating term limits for members of Congress, while all three agreed the terms of Supreme Court justices should be limited.

Kelly and Stratton said they support Medicare-for-All legislation. Krishnamoorthi has called it “an excellent goal” and said he would vote for such a bill but argues Congress must first restore Trump-era Medicaid cuts and the elimination of tax subsidies for premiums for people covered by the Affordable Care Act.

Despite those distinctions, the candidates share broad agreement on many issues. All argue that a Republican-controlled Congress has failed to check what they describe as excesses by the Trump administration. Each also contends that Trump’s war on Iran was illegal because Congress did not authorize it.

It’s always the money

But issues have largely been clouded over by constant fighting over how the contest has been funded.

In preparation for Durbin’s eventual retirement, Krishnamoorthi spent his five terms representing what’s become a safe Democratic district in the northwest suburbs, stockpiling campaign cash for a Senate run. He began the 2026 election cycle with $17.1 million in his House campaign account, nearly as much as the other 16 members of the Illinois congressional delegation combined.

As of the latest federal disclosures, Krisnamoorthi had raised nearly $30.5 million, including $19 million transferred from his House campaign fund. Only Georgia Sen. Jon Ossoff, a one-term Democrat defending a key swing-state seat, has raised more money nationwide.

In debates, Stratton has highlighted the health care industry contributions to Krishnamoorthi as a reason for him not fully embracing Medicare-for-All. The congressman — who has served as a ranking member on House Oversight subcommittees overseeing health care and related policy — has noted he’s received that financial backing due to his strong ties to the medical community, including his wife and brother, both doctors.

But he argues his large, diverse donor base gives him independence to challenge powerful players in the industry, citing work targeting high prescription drug costs, regulating vaping and reforming prescription drug intermediaries.

Stratton, who has raised nearly $4.1 million since April, has tried to make campaign finance the central issue by pledging not to accept contributions to her Senate candidate fund from corporate political action committees. It helped earn her endorsements from progressive Massachusetts Sen. Elizabeth Warren and the group End Citizens United.

But Krishnamoorthi and Kelly have labeled her a hypocrite because of corporate contributions to other committees backing her candidacy, including the Democratic Lieutenant Governors Association and Illinois Future PAC. Illinois Future, which was reported to have spent $11.8 million on ads backing Stratton and opposing Krishnamoorthi, received at least $5 million from Pritzker and more from his relatives.

In the campaign’s closing weeks, at least three other committees funded, in part, by Krishnamoorthi supporters have spent a combined $11.6 million on ads opposing Stratton but also boosting him and Kelly. The spending on Kelly’s behalf has been widely viewed as an attempt to split the Black vote between her and Stratton, potentially aiding Krishnamoorthi.

That prompted Kelly to say, “I know they’re doing this to help Raja, not to help me. I mean, I wasn’t born yesterday.”

Kelly, who’s raised $3.3 million for her campaign, two-thirds of it transferred from her House campaign fund, has defended her acceptance of corporate PAC money, saying she has demonstrated her independence from contributors.

With fewer financial resources than her rivals, Kelly aired one of her campaign’s few TV ads Tuesday, casting herself as above the fray of her bickering opponents.

“Oh, hell no,” Kelly says, walking over and then knocking over a TV showing dueling ads from Stratton and Krishnamoorthi criticizing the other. “My opponents want to attack each other while we struggle to survive.”

Lt. Gov. limitations

For Stratton, the Senate bid also reflects the political limits of the lieutenant governor’s office, a position largely defined by loyalty to the governor, with few defined duties and a job in which few people can actually name the officeholder.

Dave O’Neal quit the post in 1981 under Gov. James R. Thompson, citing boredom and saying, “A person of average intelligence could learn it in a week.” Bob Kustra, who served under Gov. Jim Edgar, sought to leave the job in 1994 to become a radio talk show host. But he stayed in the post after Edgar had heart problems — only to quit again with six months left in his second term to become a university president.

O’Neal and Kustra were the last two sitting lieutenant governors of Illinois to run for the U.S. Senate. Both Republicans, O’Neal lost to Democrat Alan Dixon in 1980, and Kustra was upset in the 1996 GOP primary by Al Salvi. Salvi, whose wife is now the state GOP chair, went on to lose the open-seat general election contest to Durbin, launching the Springfield Democrat’s Senate career.

With few individually identifiable policy achievements as lieutenant governor, Stratton has relied on what she calls the success of the “Pritzker-Stratton” administration, arguing it offers a governing model for Washington.

“This blueprint is really about what Gov. Pritzker and I have been able to accomplish over these last seven years, inheriting a state that had gone almost two years without a budget and all of the effects of that and what happened to our social service safety net and our universities and so many other ways that people were harmed by that,” she said.

“I’m proud of what we’ve done to really put us on good fiscal footing, to protect rights, to attract business, to make sure that people can have higher wages, to expand access to health care, including reproductive health care,” she said. “These are things that we have done and it is a model for what I want to take to Washington.”

Pritzker selected Stratton, a mediation attorney and a freshman member of the Illinois House, to be his running mate in the 2018 race for governor.

Two years earlier, she had defeated incumbent Democratic Rep. Ken Dunkin in the most expensive and highest-profile legislative race in the 2016 primary after Dunkin aligned himself with one-term Republican Gov. Bruce Rauner in a political battle against then-Democratic House Speaker Michael Madigan that left the state budgetless for two years.

Dunkin’s campaign received $1.3 million from a political committee run by GOP operative and right-wing radio talk show host Dan Proft. Stratton’s campaign drew broad union support and even achieved an unusual state legislative endorsement from then-President Barack Obama.

‘Kind of a radical’

A Krishnamoorthi victory would make him a junior seatmate to U.S. Sen. Tammy Duckworth, whom he unsuccessfully challenged in a 2012 Democratic primary for a U.S. House seat. When Duckworth in 2016 left the House and was elected to the Senate, Krishnamoorthi captured the suburban congressional seat.

Krishnamoorthi has sought to hew to a moderate position on business issues and concerns while looking to more progressive positions on social issues like gay rights. He said he sees himself as “kind of a radical, common-sense progressive.”

“I’m a racial, religious, ethnic minority immigrant with 29 letters in my name. I identify with people who are strivers or Dreamers, as single moms, the most vulnerable, LGBTQ people who have been bullied. I identify myself with the small businesses who constantly feel like the playing field is unlevel for them relative to big corporations,” Krishnamoorthi said.

“I’ve made a career of standing up to bullies, whether it is going after e-cigarette companies that prey on youth, whether it’s going after soup companies who poison our baby food with toxic heavy metals, whether it’s big pharmaceutical companies like Purdue Pharma who poisoned a generation of people with Oxycontin, I went after them, and because of my efforts and my office’s efforts, we were able to make a lot of progress in dealing with these scourges,” he said. “Now, we have perhaps the biggest bully of them all, Donald Trump, and I have a track record of standing up to bullies and I can stand up to him as well.”

In Congress, Krishnamoorthi highlights his efforts to expand funding for federal vocational and technical education programs and his opposition to the now-failed $25 billion Kroger-Albertsons merger, citing anti-competitive concerns about higher food prices and the potential loss of union jobs.

Kelly, a Far South Side and south suburban congresswoman whose district goes as far south as Danville, is a former state legislator, chief of staff to the state treasurer and chief administrative officer for Cook County. She lost a 2010 bid for state treasurer but won election to the U.S. House in 2013 following the resignation of Jesse Jackson Jr., who is trying to reclaim the seat this year.

A gun control advocate, Kelly has labeled her Senate campaign as “People Over Profits,” an agenda that includes capping child care costs, expanding health care and lowering housing and energy costs while raising taxes on the wealthy.

“I know I have much more experience. I’ve accomplished many things. People need to check the record, whether it’s health care, whether it’s gun violence prevention, economic development, consumer protection, neither one of them has done what I have done,” Kelly said.

“I’m an optimist,” she said. “But also I’m a realist too. I’ve been there, and I know what can pass, what we can maybe get crossover (votes from Republicans). About the attitude that I don’t have to work with them? I’ve been in Congress 13 years, only in the majority four years. Yes, you have to work with them. And people want to see that. Yes, they want to see fighters, but they want to see people that have accomplished something … It’s easy to spout out campaign slogans and platitudes, but I’m a realist. I’m there. I know the possibilities, but I also have vision and hope.”

Also seeking the Democratic nomination are Kevin Ryan, Steve Botsford Jr., Bryan Maxwell, Jonathan Dean, Sean Brown, Awisi Bustos and Christopher Swann.

On the Republican side, former Illinois GOP Chair Don Tracy of Springfield is the most noteworthy name seeking the party’s U.S. Senate nomination. He’s part of a field supporting Trump’s presidency and the administration’s immigration enforcement and pro-business moves.

Tracy lost a 2002 bid for a state Senate seat as a Democrat and in 2010 was an unsuccessful GOP lieutenant governor candidate. He gave up the state GOP chairmanship in 2024 after about 3 ½ years, citing too much internal squabbling within the party.

Also running is Jeannie Evans, an attorney billing herself as a “fresh face of the Republican Party of Illinois,” but she didn’t state she was a Republican on her website until informed by a reporter. Others running for the Republican nomination are Casey Chlebek, who unsuccessfully sought the GOP U.S. Senate nomination in 2020 and 2022; Pamela Denise Long; Jimmy Lee Tillman II; and R. Cary Capparelli.

Chicago Tribune’s A.D. Quig contributed.