Franklin D. Roosevelt began his political career in New York's state senate and served as assistant secretary of the navy from 1913 to 1920. After an unsuccessful vice-presidential campaign and the disabling illness diagnosed as polio, he rebuilt his public career and became governor of New York. His response to the Depression helped establish a national reputation, and he defeated Herbert Hoover in 1932, taking office as president amid a banking and economic emergency.

The New Deal combined banking measures, relief, public works, agricultural policy, and efforts to regulate industry. Social Security and labor legislation became enduring institutions, while other programs were struck down or revised. Roosevelt's use of radio and press conferences helped explain policy and sustain support. His proposal to enlarge the Supreme Court in 1937 met strong resistance, demonstrating limits on presidential authority. The reforms reduced hardship and changed expectations of federal responsibility, though recovery remained incomplete before wartime mobilization.

As international conflict intensified, Roosevelt supported aid to Britain and other countries while navigating neutrality laws and domestic opposition. The attack on Pearl Harbor in December 1941 brought the United States into the war. He directed mobilization and worked with Churchill and Stalin to coordinate strategy against the Axis powers. His administration also authorized the forced removal and incarceration of Japanese Americans, a major violation of civil rights. Segregation and exclusion limited the benefits and protections available to other groups within the society his policies sought to strengthen.

Roosevelt won four presidential elections and continued leadership despite declining health. Conferences including Tehran and Yalta addressed military coordination and the future international order, while planning for the United Nations sought a framework beyond wartime alliance. He died in April 1945 before the war ended. His career greatly expanded the practical scope of the presidency and the federal government's role in economic security. The record combines innovative public institutions and coalition building with coercive and discriminatory decisions. Assessing the presidency requires attention to those exclusions alongside relief, mobilization, and the attempt to construct a more stable international settlement.