John F. Kennedy
43 years, 7 months
John F. Kennedy is remembered for his vigor and glamour. But he also committed one of the worst blunders of any new president by supporting the invasion of Cuba at the Bay of Pigs in 1961.
Kennedy narrowly won the presidency in 1960 against Republican Richard Nixon, becoming the second-youngest president and the youngest ever to win the office by election.
Americans remember him as the man who was cut down in the flower of his youth before he had a chance to fulfill his potential.