It was the early 1960s, on the cusp of the sexual revolution, when a 19-year-old White House intern named Mimi Beardsley commenced a sexual relationship with President John F. Kennedy. She was not the only woman to have an affair with JFK, nor he the last President to dally with an intern. Yet the unearthing of the long-buried secret does matter. Like it or not, care or not, it's a piece of American history. Some people think it should have remained hidden. Not Mimi. Marion Fahnestock, now 60 and living on the upper East Side, confirmed her identity to the...