Another sordid case of campaign fund misuse? Sen. Mark Kirk says no.

Revelations that a formal complaint of campaign finance impropriety has been filed against US Sen. Mark Kirk (R) of Illinois threaten to embroil the first-term senator in a sordid tale of cronyism and hush money – but only if the charges made by the senator's ex-wife stick.

The Federal Elections Commission (FEC) has recently acknowledged receiving a formal complaint from Kimberly Vertolli, Senator Kirk's ex-wife, alleging that the Kirk campaign improperly funneled thousands of dollars to his then-girlfriend during the 2010 election season. Kirk had divorced Ms. Vertolli in 2009, but since then Vertolli has named the girlfriend, Dodie McCracken, as the reason for their breakup.

In 2010, Kirk won the US Senate seat previously held by President Obama. A Kirk representative has described Vertolli's allegations as "groundless" and "consisting of bitter, personal attacks." 

Vertolli's complaint also names herself as a recipient of $40,000 from the Kirk campaign, which she alleges was paid to keep her quiet about the campaign money previously directed to Ms. McCracken. 

News of the FEC complaint against Kirk came to light this week, with a report in the Chicago Tribune. Vertolli's sworn affidavit was filed with the FEC in November, the report said.

The complaint states that Kirk broke campaign disclosure laws by funneling more than $143,000 to McCracken through The Patterson Group, an advertising firm based in Wilmette, Ill. McCracken has acknowledged receiving the money, even though her name does not appear on federal disclosure filings. According to the Tribune, the senator's attorneys told the FEC that McCracken’s name did not appear because she served as a subcontractor with the Wilmette firm.

McCracken’s payment was part of the $1.85 million the Kirk campaign paid The Patterson Group. A McCracken business associate and friend owns the firm, according to the Chicago Tribune. McCracken is a former Kirk press secretary, from his days as a US congressman.

Kirk representatives deny any violation of campaign finance law and say the senator's ex-wife is acting out of spite. 

“We are saddened that she decided to file this ill-advised complaint and abuse the FEC process to air personal grievances,” Kirk campaign manager Eric Elk told the Tribune via a written statement. Mr. Elk said McCracken handled a variety of duties including media strategy, ad placement, fundraising, event planning, and celebrity endorsements.

"Like any other important member of a campaign team, McCracken made contributions on many campaign activities,” Elk said.

To establish that no wrongdoing occurred, the Kirk campaign will need to show that McCracken provided legitimate work in return for the payment, says a prominent attorney in Washington who specializes in election law, but who declined to speak for attribution because he knows some of the people involved in the FEC complaint.

“If the only revelation is [McCracken] was a partner in that firm that benefited from the distribution of those funds, it won’t matter, as long as the firm provided that much value to that campaign," the source says in a phone interview. "If they didn’t provide value to the campaign, [the complaint] will be relevant." 

FEC rules permit campaigns to make payments to a candidate's relatives or personal acquaintances. However, the candidate must prove that those individuals provided services of equal value.

The Tribune report said Kirk’s campaign also directed $40,000 to Athens & Sparta Counsel LLC, a corporate entity Vertolli says she created out of her home in Alexandria, Va., soon after joining his campaign in late 2010. She says the money was meant to keep her quiet after she criticized McCracken's role in the Kirk campaign during a Chicago Magazine interview published in August 2010.

“There wasn’t enough room for the two of us to stay in Mark’s life,” the magazine quotes Vertolli as saying. She also described McCracken as a “very pernicious force on his team who is wielding a disproportionate amount of negative influence on him.”

If it is proved that the Kirk campaign is the source of the $40,000, Kirk will need to establish that the money was for the purpose of influencing the election and not for personal use, the Washington source says.

Elk told the Tribune that Vertolli’s role in the campaign was “to assist with legal research projects, including reviewing FEC reports, opposition research and monitoring campaign developments for legal issues.”

The charges of diverting campaign funds for personal use are somewhat akin to those facing John Edwards, the 2008 presidential candidate from North Carolina who is currently on trial for alleged violations of federal campaign finance laws. Mr. Edwards argues that the nearly $1 million paid to a mistress by two wealthy patrons were personal gifts, not political contributions, and so not subject to federal election law.  

Kirk has not made any public appearances since January, when he was diagnosed as having suffered a stroke. He is no longer involved in a relationship with McCracken. His website shows him in rehabilitation, but it's not known when he will return to work in the Senate.