In recognition of the President's Day holiday, we revisit last year's conversation with best-selling author Kenneth C. Davis, who tells us about some of the least-known presidents of all-time from James Polk, the only speaker of the House of Representatives ever to be elected president, to William McKinley, the third of four presidents to die at the hands of an assassin. Davis's latest book is "Don’t Know Much About The American Presidents." Original air date 02/18/13