Biden exchanges verbal blows with audience member at Iowa town hall: ?You?re a damn liar, man?

Democratic presidential candidate Joe Biden blasted a man at an Iowa town hall as a?damn liar Thursday -- and challenged him to a push-up contest --?after he accused the 77-year-old former vice president of being too old and took a swipe at son?Hunter's?role on the board of a controversial?Ukrainian natural gas firm.