Before Pearl Harbor, Americans feared foreign invasions, air raids, biological weapons, and, conversely, the prospect of a dictatorship being established in the United States. To protect Americans from foreign and domestic threats, Franklin D. Roosevelt warned Americans that the world has grown so small and eventually established the precursor to the Department of Homeland Security-an Office of Civilian Defense (OCD). As its head, FDR appointed New York City Mayor Fiorello La Guardia; First Lady Eleanor Roosevelt became its assistant director. Defenseless Under the Night argues that the politics of national vulnerability are traceable to the rise of fascist threats during world war II. It shows how the debate about home defense was actually a debate about the direction of New Deal liberalism after 1938. While La Guardia used the government to protect the country against foreign attack and militarize the civilian population (national security liberalism), Eleanor Roosevelt insisted that the OCD should primarily focus on establishing a wartime New Deal, what she and her allies called social defense. The book reveals how social defense liberals saw the war as a chance to mobilize the grassroots through Washington to meet social needs, while La Guardia prioritized peoples physical safety, with consequences for postwar liberalism. It explores constitutional questions about civil liberties, the role and power of government propaganda, the Blitzs impact on U.S. politics and policy, and competing liberal visions for American national security.