The gun control group Americans for Responsible Solutions revoked their endorsement of Illinois Republican Senator Mark Kirk on Saturday after he mocked his opponent’s heritage last week.

On October 27 during a debate, U.S. Representative Tammy Duckworth mentioned her ethnic and military background, explaining how her family has served this country for decades. Kirk’s response: “I’d forgotten that your parents came all the way from Thailand to serve George Washington.”

Duckworth was born in Bangkok; her mother is Thai, her father American. Duckworth lost both her legs while serving in Iraq as a Black Hawk helicopter pilot for the U.S. Army. She was even awarded the Purple Heart.

Kirk was widely criticized for his comment and apologized on Twitter the next day.

Sincere apologies to an American hero, Tammy Duckworth, and gratitude for her family's service. #ilsen

— Mark Kirk (@MarkKirk) October 28, 2016

Americans for Responsible Solutions, headed by former Democratic Congresswoman Gabby Giffords, announced that they could no longer support Kirk. The group’s executive director, Peter Ambler, gave the official statement.

“In public office, your values matter as much as your votes. That’s the example Gabby set in Congress and in her campaigns, and that’s the example we must follow in the movement to reduce gun violence.

Senator Kirk’s racist attack on Congresswoman Duckworth is unacceptable and represents a low point, even in this election season. For that reason, Americans for Responsible Solutions PAC is revoking its endorsement of Senator Kirk.”

Americans for Responsible Solutions originally endorsed Kirk because of his support for moderate gun control. The group also recognized the need for bipartisan support to achieve its goals.

However, after the Kirk’s comments, Americans for Responsible Solutions said it will now support Duckworth.

“While we believe the path to responsible change and communities safer from gun violence must include Republican champions, we cannot continue to support Senator Kirk. A man who is not worthy of your vote cannot be worthy of our endorsement. As Gabby and Mark wrote in August, Congresswoman Duckworth is an American hero and a powerful voice for stronger gun laws. She will be an exceptional United States Senator.”