Some leaders know which moments or decisions in their lives will lead all biographies of their lives. Winston Churchill knew that his leadership during World War II would be the central theme of all future historians looking at his life. John F. Kennedy understood that his handling of the Cuban Missile Crisis would define his role in the history books: If he messed that up, nothing else would matter. President Barack Obama knows that historians will remember him as the person who finally achieved health care reform, and he is hoping to add immigration reform to the list, even though he has probably spent more of his time dealing with economic and foreign policy issues. For Churchill, the dominant role of his war leadership is appropriate, but in the case of Kennedy and...