In a stunning moment during a Thursday night debate, an embattled U.S. senator cast doubt on his opponent’s military and ethnic heritage.

Rep. Tammy Duckworth (D-Ill.), seeking to unseat Sen. Mark Kirk (R) in Illinois, invoked her family’s military service while answering a debate question.

“My family has served this nation in uniform going back to the Revolution,” Duckworth said. “I am a daughter of the American Revolution. I’ve bled for this nation. But I still want to be there in the Senate when the drums of war sound. Because people are quick to sound the drums of war, and I want to be there to say this is what it costs, this is what you’re asking us to do. . . . Families like mine are the ones that bleed first.”

Kirk was offered a chance to rebut. “I’d forgotten that your parents came all the way from Thailand to serve George Washington,” he said.

Duckworth’s mother, Lamai, is Thai, but her late father, Franklin, was a Marine veteran whose family roots in this country trace to before the American Revolution. Tammy Duckworth was severely wounded in the Iraq War, losing her legs while serving as a helicopter pilot.

The moderator moved on to the next question, but a panelist gave Duckworth time to respond by detailing her family history — including the fact that the Daughters of the American Revolution erected a statue of her in Mount Vernon, Ill.

Democrats immediately slammed Kirk for the attack. A spokeswoman for the Democratic Senatorial Campaign Committee called the remark “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,” said the spokeswoman, Lara Sisselman.

A statement issued Thursday night by Kirk campaign spokeswoman Eleni Demertzis did not include an apology from the senator or any claim that Duckworth has misrepresented her family heritage.

“Senator Kirk has consistently called Rep. Duckworth a war hero and honors her family’s service to this country,” Demertzis said. “But that’s not what this debate was about. Rep. Duckworth lied about her legal troubles, was unable to defend her failures at the VA and then falsely attacked Senator Kirk over his record on supporting gay rights.”

Kirk has faced an uphill fight in one of the nation’s most reliably Democratic states, and he has faced questions about whether he has exaggerated his own military record. Recent polls have shown Duckworth with a significant lead.

Update: Kirk apologized to Duckworth in a Friday tweet.