While all four relationships were costly, Teddy Kennedy's late-night assignation with campaign worker Mary Jo Kopechne, and her subsequent death after he drove his car off a pier in Martha's Vineyard, likely cost him the presidency. Kennedy decided not to run in 1972 and 1976, and his last stand on the presidential stage was a 1980 primary battle that he lost to Jimmy Carter. His defeat in 1980 was partially due to a devastating interview with Roger Mudd in which the newsman grilled Kennedy on -- you guessed it -- Chappaquiddick.