In January 2008, McCaskill endorsed then-Senator Barack Obama in his campaign for the Democratic nomination for president, making her one of the first Senators to do so. She was one of the most visible faces for his campaign, and her support was crucial to Obama's narrow victory in the Missouri primary in February 2008. She has credited her daughter Maddie as having persuaded her to publicly endorse Obama. She was frequently mentioned as a possible vice-presidential nominee for Obama, but was never seriously considered. She spoke on the opening day of the Democratic National Convention in August 2008.