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Duckworth's paternal ancestors served in the American Revolution

Kirk has also faced criticism for misrepresenting his military career

Washington CNN  — 

Sen. Mark Kirk apologized Friday to his Democratic challenger Rep. Tammy Duckworth after using her Thai heritage to deride her family’s military history during a debate.

“Sincere apologies to an American hero, Tammy Duckworth, and gratitude for her family’s service. #ilsen,” he tweeted.

Duckworth accepted the apology, writing on Twitter, “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.”

The Illinois Republican questioned the military veteran’s ties to the American Revolution during a Senate debate Thursday.

Duckworth was speaking about how her father’s family served in the military since the American Revolution.

“My family has served this nation in uniform going back to the Revolution. 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 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,’” she said at the University of Illinois Springfield.

“Families like mine are the ones that lead first. But let’s make sure the American people understand what we’re engaging in. And let’s hold our allies accountable because we can’t do it all,” she added.

Kirk responded: “I forgot your parents came all the way from Thailand to serve George Washington.”

When he said that, Duckworth was drinking a bottle of water and put it back on the table as he finished his sentence. She smiled and the moderator moved on to the next question.

“Sen. Kirk’s statement speaks for itself, as does Tammy’s response,” Duckworth campaign spokesman, Matt McGrath, told CNN after the debate.

Kellyanne Conway, the campaign manager of Donald Trump – whom Kirk has publicly broken with – mocked the Illinois senator over the episode, linking to a story about the debate and tweeting, “The same Mark Kirk that unendorsed his party’s presidential nominee and called him out in paid ads? Gotcha. Good luck.”

Duckworth was born in Thailand, but her father was a Marine veteran who traced his family’s American roots to before the Revolutionary War. She is an Iraq War veteran who lost her legs and partial use of her right arm during a mission and was awarded a Purple Heart.

In the past, Kirk has also faced criticism for misrepresenting his military career. In 2010 he accepted responsibility misstatements about his Navy Reserve career, including that he served in the Gulf War, that he once commanded the Pentagon war room and that he came under fire while flying intelligence missions over Iraq.

And in 2016, Kirk falsely asserted on his campaign website that he was a veteran of the Iraq War. He actually stayed in the United States during the Iraq War when he served in the Navy Reserves.

Duckworth’s opponents have faced criticism over their attacks on her. In 2012 then-Rep. Joe Walsh – who is facing criticism this week after saying he’s going to pick up a musket if Donald Trump loses the 2016 election – attacked Duckworth over her war record, saying she talks too much about her war record.

CNN’s David Mark contributed to this report.