LOUISVILLE, Ky. — Sen. Mitch McConnell, already facing what could be the toughest election in his career, lost his campaign manager Friday night.

The manager, Jesse Benton, issued a statement just after 6 p.m., abruptly announcing his departure and citing reports about his “role in past campaigns.” Benton was referring to his job as a senior official in former Rep. Ron Paul’s 2012 presidential campaign, which paid an Iowa state senator to switch his support from Rep. Michele Bachmann to Paul right before the state’s caucus.

The state senator, Kent Sorenson, who resigned last year, pleaded guilty in Iowa Wednesday to obstruction-of-justice charges stemming from the bribery scandal. He acknowledged accepting $73,000 from Paul’s campaign to drop his support for Bachmann.

Benton has not been implicated in the case, but his position in Paul’s campaign has revived questions about what he knew about the bribe, and the case put McConnell, the Senate minority leader, on the defensive.

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“I cannot, and will not, allow any possibility that my circumstances will affect the voters’ ability to hear his message and assess his record,” Benton said of McConnell.

“This decision breaks my heart, but I know it is the right thing for Mitch, for Kentucky and for the country,” Benton added.

The resignation, effective Saturday, comes barely two months before Kentucky voters choose between McConnell, a five-term incumbent and the top-ranking Senate Republican, and Democratic challenger Alison Lundergan Grimes.

Polls show McConnell and Grimes to be neck and neck in a race that could play a role in determining if Democrats retain control of the Senate.

In the Iowa case, prosecutors refused to say who paid Sorenson.

Benton, a tea-party insider, said he has been the target of “inaccurate press accounts and unsubstantiated media rumors” about his role in past campaigns that are “politically motivated, unfair and, most importantly, untrue.”

Separately Friday, McConnell’s campaign said the senator “obviously has nothing to do with the Iowa presidential caucus or this investigation, so it would be inappropriate for his campaign to comment on this situation.”

Charly Norton, a spokeswoman for the Grimes campaign, said: “Sen. McConnell owes the people of Kentucky a full account of what he knew and when he knew it.”

Benton was mentioned in documents gathered during an Iowa state ethics probe of Sorenson, a complaint to the Federal Election Commission and emails purported to be from the Ron Paul campaign obtained by the nonpartisan Center for Responsive Politics, which monitors federal campaign-finance issues, The Courier-Journal of Louisville reported.

Benton’s hiring to oversee McConnell’s campaign was seen as a way to appeal to more conservative elements of the Kentucky GOP.

McConnell eventually faced a tea-party-inspired opponent in the Republican primary, which he easily won.

Early in the campaign, Benton gained unwanted attention with the airing of a recording in which he was heard saying he was “holding my nose” to work for McConnell’s re-election campaign.

Benton managed Rand Paul’s successful U.S. Senate campaign in Kentucky in 2010. Rand Paul is Ron Paul’s son.