Illinois U.S. Sen. Mark Kirk apologized Friday morning for a comment he made about his opponent’s ethnic heritage during a debate. 

“Sincere apologies to an American hero, Tammy Duckworth, and gratitude for her family’s service,” Kirk wrote in a tweet. 

Duckworth, an Iraq War veteran of mixed Chinese and Caucasian heritage, had cited during the debate her family’s history of military service in the U.S., saying it dated back to the American Revolution. Kirk responded with sarcasm, saying he’d “forgotten” Duckworth’s “parents came all the way from Thailand to serve George Washington.”

Duckworth, an Iraq War veteran who lost both legs when the Black Hawk she was piloting was shot down in 2004, was born in Bangkok. Her mother, who is of Chinese descent, was born in Thailand. Duckworth has said her father first went to Southeast Asia while serving with the Marines in Vietnam.

Kirk’s comments drew heavy scorn across social media. Democratic presidential nominee Hillary Clinton posted on Twitter that she is thankful for Duckworth’s and her family’s service, adding: “It’s really not that hard to grasp, Mark Kirk.”

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Donald Trump’s campaign manager also took the opportunity to jab at Kirk, who earlier this year withdrew his support for the GOP presidential nominee and has been a vocal critic.

“The same Mark Kirk that unendorsed his party’s presidential nominee and called him out in paid ads? Gotcha. Good luck,” Kellyanne Conway posted on Twitter late Thursday.

Locally, the comment upset many Asian-American voters, of both political affiliations.

“I’m the diehard Republican. I support almost the party line on the Republican,” said Charles Jung, a Korean-American small business owner and president of an organization that encourages Korean-Americans to vote. “But after I heard about this incident, I have to reconsider what I’m going to do.”

Jung said that as an immigrant, he found Kirk’s remark hurtful.

“Most immigrant people are contributing to American society, regardless of where they’re coming from,” he said.

Jung added that an apology from Kirk could win back his vote, though he would have to consider it carefully.

“I found it to be very racist,” said OiYan Poon, assistant professor of higher education at Loyola University. “He was essentially suggesting, without saying in so many words, that the Congresswoman’s heritage undercut any value of her service.”

Poon added that the remark further added to a growing, and sometimes heated, discussion during this election season of what it means to be American.

“I think even in 2016 we still see that if you are not of white, European descent — or appear to be of white, European descent — then your American-ness or your belonging-ness in this nation is questioned,” Poon said. “I think the Senator is realizing with his apology that with the changing demographics, you can’t make these kind of comments anymore.”

Asian Americans are the fastest-growing racial group in Illinois, making up about 5 percent of the population. Though they have historically had low election turnout there has been an increased focus within its various communities in recent years to register and get voters to the polls. A recent national survey found that Asian Americans are twice as likely to identify themselves as Democrats than as Republicans.

“I think the comment really points at this insidious stereotype of Asian Americans as the perpetual foreigner,” said Tuyet Le, executive director of Asian Americans Advancing Justice Chicago. 

“One, that we’re a part of the discussion, I think, is great,” Le continued. “But two, there is still this back and forth of how relevant we are, how we feel on these different issues and whether we can and should be taken seriously.”

“I think I may walk over and early vote today. That’s what that’s inspired me to do,” said Laura Kina, Professor of Art, Media, & Design at DePaul University and Director of Critical Ethnic Studies and the vice-president and co-founder of the Critical Mixed Race Studies Association. Kina, herself of mixed heritage, including Asian, said she hoped other Asian American will also respond by going to the polls. “Whatever their leanings. You need to vote. It matters.”

Kirk, who suffered a stroke in 2012 and returned to work one year later, is seen as one of the Senate’s most vulnerable Republican incumbents.

Kirk has complicated his own re-election bid with his tendency to make off-color statements. In August, he said Obama was acting like the “drug dealer in chief” when the U.S. made a $400 million payment to Iran contingent on the return of U.S. prisoners.

He apologized in 2015 after referring to South Carolina U.S. Sen. Lindsey Graham, who’s unmarried, as a “bro with no ho.”

During his first bid for Senate in 2010, Kirk acknowledged that he had exaggerated some of his own military record, including stating that he came under enemy fire while flying reconnaissance missions in Iraq as a Navy intelligence officer.

The Associated Press contributed to this report.

Odette Yousef is a WBEZ reporter. Follow her @oyousef and @WBEZoutloud.