Monday marks the 100th birthday of John Fitzgerald Kennedy, the nation's 35th President, whose tenure was tragically cut short by his assassination in 1963. Despite only three years in office, polls of historians continually rank JFK among the top 10 presidents in American history, with his handling of Cold War crises, pushing space exploration all the way to the moon, launching the Peace Corps and inspiring public service. But as NewsHour Weekend Special Correspondent Jeff Greenfield reports, the aftermath of Kennedy's death has given historians almost as much to study about American society and its undercurrents as JFK's life.