Tough, concerned, direct, occasionally vulgar, and often partisan--Harry S. Truman would never completely work himself out from the shadow of Franklin Delano Roosevelt. Yet Truman partly commands our attention because he was the successful executor of Roosevelt's remarkable political estate.

It is not too much to suggest that the Truman administration, along with that of FDR, constituted the most important turning point in recent U.S. history. During the Roosevelt administration the American state system had changed dramatically: the federal government had rapidly become ascendant over...