GOP Sen. Mocks Biracial Opponent's US Heritage in Illinois Senate Debate

A Republican Senator questioned his opponent's ties to the U.S.

In the 30-second time slot given to him for rebuttal, Kirk kept his remarks to just one sentence.

The race is seen as critical for Republicans, who are struggling to hold on to enough seats to keep their Senate majority after the November election. Recent polling conducted by Southern Illinois University puts Duckworth ahead by 14 percentage points. Previous polls showed Duckworth with a slight lead.

Kirk sent out a flurry of post-debate tweets, one of which called Duckworth "one of the least effective members of Congress."

Duckworth tweeted a photo of herself with her parents and wrote, "my dad and his family have served this nation in uniform since the Revolution."