A new history shows how FDR developed a vision of national security focused not just on protecting Americans against physical attack but also on ensuring their economic well-being—and how the nascent conservative movement won the battle to narrow its meaning, durably reshaping US politics. Americans take for granted that national security comprises physical defense against attacks. But the concept of national security once meant something more. Franklin Roosevelt’s vision for national security, Peter Roady argues, promised an alternate path for the United States by devoting as much attention to economic want as to foreign threats. The Contest over National Security shows how a burgeoning conservative movement and power-hungry foreign policy establishment together defeated FDR’s plans for a comprehensive national security state and inaugurated the narrower approach to national security that has dominated ever since. In the 1930s, Roosevelt and his advisors, hoping to save the United States from fascism and communism, argued that national security entailed protection from both physical attack and economic want. Roosevelt’s opponents responded by promoting a more limited national security state privileging military defense over domestic economic policy. Conservatives brought numerous concerns to bear through an enormous public relations offensive, asserting not just that Roosevelt’s plans threatened individual freedom but also that the government was less competent than the private sector and incapable of delivering economic security. This contest to define the government’s national security responsibilities in law and in the public mind, Roady reveals, explains why the United States developed separate and imbalanced national security and welfare states, with far-reaching consequences. By recovering FDR’s forgotten vision, Roady restores a more expansive understanding of national security’s meanings as Americans today face the great challenges of their times.