This book offers the first comprehensive account of the politics of countersubversion in the United States prior to the McCarthy era. The book traces the course of American countersubversion over the first half of the twentieth century, culminating in the rise of McCarthyism and the Cold War. This sweeping study explores how anti-subversive fervor was dampened in the 1920s in response to the excesses of World War I, transformed by the politics of antifascism in the Depression era, and rekindled in opposition to Roosevelt's ambitious New Deal policies in the later 1930s and 1940s. Varied interest groups such as business tycoons, Christian denominations, and Southern Democrats as well as the federal government pursued their own courses, which alternately converged and diverged, eventually consolidating into the form they would keep during the Cold War. Rigorous in its scholarship yet accessible to a wide audience, this book shows how the opposition to radicalism became a defining ideological question of American life.