Sen. Mark Kirk (R-IL) mocked the mixed-race background of Democratic challenger Rep. Tammy Duckworth (D-IL) during a Thursday night debate.

Duckworth, a U.S. Army veteran who lost both legs in the Iraq war, was born in Thailand to a U.S. Marine father and a Thai-Chinese mother.

At the Senate debate, she touched on her background, speaking about her family’s history of military service.

Tammy Duckworth is a vet who lost both legs in Iraq. Her family has served since the Revolutionary War. And yet… pic.twitter.com/DHd3kWrUsN — Anthony Breznican (@Breznican) October 28, 2016

“My family has served this nation in uniform, going back to the Revolution,” Duckworth told the audience at the University of Illinois Springfield. “I’m 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. And if that’s the case, I’ll go. Families like mine are the ones that bleed first.”

“I had forgotten that your parents came all the way from Thailand to serve George Washington,” Kirk replied sarcastically.

Duckworth said nothing, moving a bottle of water on the table and turning to look at Kirk. The debate moderator quickly moved on to the next question.

After the event ended, the Illinois congresswoman tweeted a photograph of her family in which she and her father are wearing military uniforms.

My mom is an immigrant and my dad and his family have served this nation in uniform since the Revolution #ILSEN pic.twitter.com/ehEBHswFMs — Tammy Duckworth (@TammyforIL) October 28, 2016

The condemnation of Kirk’s remark was swift.

Wow, Sen. Mark Kirk really flubbed his debate tonight with Tammy Duckworthhttps://t.co/bcjLMckP2D — Taegan Goddard (@politicalwire) October 28, 2016

Is there any interpretation of the Mark Kirk quote in which he’s not being racist? I don’t think so but I want to hear the pitch. — Dave Weigel (@daveweigel) October 28, 2016

To be clear, GOP Sen. @MarkKirk just questioned the Revolutionary War service of Tammy Duckworth’s family because she is of mixed heritage. — Brandon Friedman (@BFriedmanDC) October 28, 2016

The Kirk campaign sent NBC a statement that did not apologize for the comment, but instead criticized Duckworth.

“Senator Kirk has consistently called Rep. Duckworth a war hero and honors her family’s service to this country,” Kirk spokesperson Eleni 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 previously admitted to lying about and misrepresenting his own military record, falsely claiming that he received an award for “Intelligence Officer of the Year” and that he served in Iraq during the war. He actually served stateside in the Navy reserves.

The Illinois senator has a history of making inappropriate comments, once calling President Barack Obama the “drug dealer in chief” for offering cash payment to Iran in exchange for the release of American prisoners, and speaking of black neighborhoods as “the one we drive faster through.”

Kirk currently trails Duckworth 38.3 percent to 47 percent, according to TPM’s PollTracker Average.