In December 1962, Da Vinci's Mona Lisa set sail from Paris to New York for what was arguably the riskiest art exhibition ever mounted. The fragile icon traveled like a head of state, with armed guards and military surveillance, in a temperature-controlled vault. Masterminding the entire show was First Lady Jacqueline Kennedy, who tirelessly campaigned to persuade National Gallery Director John Walker, French President Charles de Gaulle, and her own...