After serving for three months as vice president, Harry S. Truman, at age 60, suddenly inherited the White House. The nearly eight years that followed were unusually turbulent—marked by victory in the wars against Germany and Japan, the first use of an atomic weapon and the development of far deadlier weapons, the Cold War, the Red Scare, the Marshall Plan, and the fateful decision to fight a land war in Korea. How did Truman become the steadfast leader who, in the rush of events, helped shap...