In the competitive Democratic primary for the 6th Congressional District, Sean Casten scored a narrow victory over six other candidates vying to take on GOP Rep. Peter Roskam.
Now, questions about how his primary campaign was financed have emerged.
One of the resources the Casten campaign used was a political action committee called "My Committee," according to a filing with the Federal Election Commission.
"My Committee" funded attack ads on another Democratic candidate in the race, Kelly Mazeski. As a super PAC, the committee is permitted to raise unlimited sums of money and has no cap on spending either - but federal election law prohibits super PACs from coordinating efforts with the candidate they're supporting.
That rule brings "My Committee" under scrutiny, as a key supporter was Casten's father Tom Casten, who records indicate donated $150,000 to the super PAC, which was previously called the "Sunshine PAC."
Politico noted after the primary that Casten "benefited from last-minute super PAC spending," adding that "a flurry of negative mailers attacking Mazeski hit the district right before the election."
Mazeski received the endorsement of EMILY's List, as well as U.S. Reps. Jan Schakowsky and Cheri Bustos, and maintained a strong on-the-ground organization.
Casten received 1,790 votes more than Mazeski, who came in second in the wide field of seven candidates.
The attack ads against Mazeski are likely to become an issue in the general election, as incumbent Peter Roskam looks to hold on to his seat.
Roskam has been targeted by Democrats as one of the most vulnerable Congressional Republicans, in a district that Hillary Clinton won in the 2016 presidential election - making the race one to watch nationwide.
New polling released by Casten's campaign on Wednesday indicated that the race appears to be a dead heat, with Roskam polling at 45 percent to Casten's 44.
And when it comes to Casten's finances, Republicans are already on the attack.
"Sean Casten using his daddy’s money to ensure that a qualified female candidate has no shot to make it out of a primary is both unoriginal and deeply concerning," National Republican Congressional Committee spokeswoman Maddie Anderson said in a statement.
"In the so-called ‘year of the woman’ – it’s a shame that Casten resorted to attacking Kelly Maseski using dark money once he realized his own message wasn’t enough to carry him across the finish line," she added.
But a spokesman for Casten said, "There was no coordination between father and son, we knew the rules and did not cross them."
“When dark money was spent against Sean in the primary, his dad set up a PAC to respond," spokesman Michael Garton said. "We had nothing to do with it and there was no coordination. The same cannot be said about ROSKAMPAC — a PAC that Peter Roskam personally established. He used that PAC to raise $1.5 million from special interests, which he directed to his Republican colleagues to win their votes for a leadership position. He still lost.”
“The truth is that our campaign finance system is broken and needs reform," Garton continued. "That’s why Sean has pledged to vote in Congress to overturn Citizens United, the wrongheaded Supreme Court decision that allows wealthy individuals and corporations to spend unlimited amounts of money in our elections. After raising tens of millions from special interests that come before his Ways and Means Committee, Peter Roskam likes the system just the way it is."