CHICAGO (AP) —U.S. Sen. Mark Kirk of Illinois apologized Thursday through a spokeswoman after being caught on a live microphone using a word that’s disparaging to women.

Kirk, who is seeking re-election in 2016, called fellow Republican senator and presidential candidate Lindsey Graham a “bro with no ho,” remarks captured on a live microphone as a U.S. Senate panel conducted a roll call vote in Washington. Graham, of South Carolina, is a lifelong bachelor who’s recently joked he could have a “rotating first lady” if elected to the White House.

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“That’s what we’d say on the …” Kirk goes on to say. The rest of the sentence is muffled, but he seems to say “South Side,” a reference to a swath of heavily minority Chicago neighborhoods that stretches south of downtown.

Kirk lives in the Chicago suburb of Highland Park.

Kirk told Politico on Thursday that he regretted the remarks, but didn’t elaborate. He later apologized through a spokeswoman.

“Senator Kirk was joking with his colleague and immediately apologized to anyone offended by his remark,” spokeswoman Danielle Varallo said in an email to The Associated Press.

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But the comments blew up on Twitter and immediately drew criticism from fellow lawmakers.

U.S. Rep. Tammy Duckworth, a Democrat running for Kirk’s seat, said Kirk needs to improve his record on women. In a fundraising email for Duckworth, Democratic U.S. Rep. Jan Schakowsky deemed it “sexist.”

“Senator Kirk’s `joke’ is as offensive as it is unfunny, and he should apologize, personally and immediately,” Kaitlin Fahey, Duckworth’s campaign manager said in a statement.

It’s not the first time Kirk’s comments have raised eyebrows.

In 2013, Kirk was harshly criticized by Democratic U.S. Rep. Bobby Rush of Chicago when he called for the arrest of up to 18,000 Gangster Disciple members. Afterward, as part of a pledge to fully understand the link between gangs and violence, he agreed to go on a police ride-along through the South Side.

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