The Human Rights Campaign (HRC), the nation's largest LGBT rights group, is under fire for its continued support of Illinois Senator Mark Kirk, a Republican, after he made a racially charged remark.

At a debate on Thursday, Kirk took a swipe at his Democratic opponent, Representative Tammy Duckworth, after she talked about her family's military history.

“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,” Duckworth said. “Families like mine are the ones that lead first.”

“I've forgotten that your parents came over all the way from Thailand to serve George Washington,” Kirk said.

Duckworth has a Thai mother and an American father who is a World War II veteran and traces his heritage back to the American Revolution, according to Mother Jones.

Kirk apologized on Friday in a tweet. “Sincere apologies to an American hero, Tammy Duckworth, and gratitude for her family's service,” he messaged, a reference to Duckworth, who lost both her legs serving in the Iraq War.

“I think that any organization would reconsider an endorsement of a candidate that makes an obvious racist statement,” said Stampp Corbin, a gay Democratic activist and publisher of San Diego LGBT Weekly.

Corbin noted that Kirk dropped his endorsement of Donald Trump, the GOP presidential nominee, over racist remarks.

“HRC needs to hold Kirk to his own standard,” he said.

In a statement, HRC called Kirk's comments “wrong and inappropriate” and called on the Republican senator to rescind them, but added that it endorsed Kirk “based on the strength of his record on LGBTQ equality” and “that remains unchanged.” Kirk was the second sitting Republican senator to endorse marriage equality and is a co-sponsor of the Equality Act, a stalled bill that would prohibit discrimination in seven key areas, including employment, housing and public accommodations, on the basis of sexual orientation and gender identity.

Critics, however, point out that Duckworth is also a strong supporter of LGBT rights.