(CBS) – The final debate between U.S. Sen. Mark Kirk and his Democratic challenger, Rep. Tammy Duckworth, featured an apology by the Republican incumbent – and a surprising contrast between the candidates on GOP presidential hopeful Donald Trump.

Kirk tried mightily Friday to recover from what may have been the biggest misstep of his campaign – when he made a remark about Duckworth’s family heritage.

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“I would like to take this moment to thank Tammy for accepting my apology my remark when I disparaged her family’s admirable military record,” the Republican said at the final U.S. Senate debate, which was sponsored by ABC 7.

In the remarks, Kirk said he didn’t know Duckworth’s family had come from Thailand to serve with George Washington — a comment critics called racist.

“I am absolutely not a racist,” Kirk said. When pressed about why he would make such a remark, he said: “I wasn’t thinking.”

Countered Duckworth: “He often says things he doesn’t think through. This is after a man who said we drive faster through African-American neighborhoods. He recently called the president the ‘drug dealer in chief.’”

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In the wake of Kirk’s stroke and Duckworth’s loss of her legs when her helicopter was shot down in the Iraq War, a reporter asked if each was healthy enough to serve.

“I have released a letter from my doctor that said from my stroke I have made a complete mental recovery. I’m also training to climb the Willis Tower for the fifth time,” Kirk said.

Duckworth: “I actually just finished the Chicago Marathon. I actually had so much fun going through all the Chicago neighborhoods. It’s my fourth marathon.”

The two said they would have different approaches if Trump defeats Democrat Hillary Clinton to win the presidency.

“If Donald Trump is elected president of the United States, then you work with him,” Duckworth said.

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Said Kirk, who has distanced himself from his fellow Republican: “I think I’m toast with him right now.”