Illinois Republican Sen. Mark Kirk made an ill-advised jab about the birthplace and ancestry of his Democratic opponent, Rep. Tammy Duckworth, during a debate on Thursday.

Duckworth, who is challenging Kirk for his seat, had just finished talking about her military service and that of her ancestors, dating back to the Revolutionary War.

“I forgot that your parents came all the way from Thailand to serve George Washington,” Kirk said in the debate at the University of Illinois Springfield.

It was an odd comment from a senator who has a reputation for making odd comments, but particularly impolitic given his opponent’s backstory. Duckworth was born in Thailand to an U.S. Marine father and a Thai mother of Chinese descent.

Duckworth and her family moved to the U.S. when she was a teenager. She went on to join the military and served in the Iraq War, where she lost both legs and earned a Purple Heart, among other commendations.

“There’s been members of my family serving in uniform on my father’s side going back to the Revolution,” Duckworth said, adding that she is a member of the Daughters of the American Revolution.

“I’m proud of both my father’s side and my mother, who is an immigrant,” Duckworth said.

Democrats quickly pounced on Kirk’s comment. Democratic Senatorial Campaign Committee spokeswoman Lara Sisselman said in a statement that the senator’s “attack ... was offensive, wrong, and racist.”

“A struggling political campaign is no excuse for baseless and despicable attacks, and Senator Kirk owes Congresswoman Duckworth and her family an apology,” Sisselman said.

Kirk campaign spokeswoman Eleni Demertzis did not apologize for the remark in a statement defending the senator.

Kirk, a former intelligence officer in the U.S. Naval Reserve, was caught making multiple embellishments and misstatements about his military record, including where he served. He said during the debate that those mistakes paled in comparison to allegations that Duckworth mishandled problems as director of the Illinois Department of Veterans Affairs.

“My past misstatements of my record have been small and selfish and I only hurt myself, I didn’t hurt veterans like my opponent,” Kirk said.

Kirk also responded to the Chicago Tribune’s endorsement of Duckworth. The paper questioned whether Kirk can still “perform to the fullest the job of a U.S. senator” after his 2012 stroke, wondering if his health has contributed to controversial comments he’s made since.

“I would say that the stroke has made me much stronger as a senator,” Kirk said in the debate. “When you come through something as difficult as a stroke you get in there and you’re going to fight, fight, fight to make sure you deliver for the people of Illinois.”

Duckworth said she thinks Kirk is “perfectly capable of doing his job.” He interrupted with a joke.

“I would say we both agree on one key point: that we both agree the next senator of Illinois should use a wheelchair,” Kirk said.

Kirk gave no clarity during the debate on whom he will support for president, other than to reiterate that he revoked his endorsement of Republican presidential nominee Donald Trump in June. Kirk said Wednesday he didn’t know who he was voting for.

Duckworth said she already cast an early ballot for Democratic presidential nominee Hillary Clinton.

According to HuffPost Pollster, which aggregates publicly available polls, Duckworth leads Kirk by nearly 9 points.

UPDATE: Oct. 28 ― Kirk apologized to Duckworth on Twitter on Friday afternoon, more than 12 hours after he made the remark.

Sincere apologies to an American hero, Tammy Duckworth, and gratitude for her family's service. #ilsen — Mark Kirk (@MarkKirk) October 28, 2016

On Friday afternoon, Duckworth thanked Kirk for the apology.

Thanks, Sen. Kirk. Let’s honor my family’s service - and your own - by sticking to the issues for the final week. See you Friday in Chicago. https://t.co/INdBtm5K3G — Tammy Duckworth (@TammyforIL) October 28, 2016