As the only president elected to four terms and who saw the country through two of its greatest cataclysms — the Great Depression and World War II — biographies of Franklin Roosevelt were certain to treat him as a magnificent figure of enduring accomplishment. In many respects he deserves this exalted regard: He transformed American government in fundamental ways, led the nation in the Second World War, created the building blocks for the postwar world order and left behind the durable New Deal Democratic Party coalition that dominated American politics for most of the next half-century, ending more than 70...