Donald Rumsfeld began his public career after naval service, staff work in Congress, and private business. Elected to the House of Representatives from Illinois in 1962, he served from 1963 to 1969. Richard Nixon appointed him director of the Office of Economic Opportunity, where he sought changes to federal antipoverty administration. He later led the Cost of Living Council and became ambassador to NATO in 1973. Under Gerald Ford he served as White House chief of staff before becoming secretary of defense in November 1975.

During his first Pentagon tenure, Rumsfeld emphasized military readiness, modernization, and concern about Soviet capabilities. He served until the change of administration in 1977. Returning to business, he became chief executive of G. D. Searle and later held leadership roles at other corporations. As a Reagan administration envoy in 1983, he visited Saddam Hussein's government in Iraq while Washington sought to limit Iranian influence during the Iran-Iraq War.

George W. Bush appointed Rumsfeld secretary of defense again in 2001. He advocated transforming the armed forces through technology, mobility, and smaller deployable formations. After the September 11 attacks he directed the initial campaign in Afghanistan and became a leading advocate and administrator of the invasion of Iraq in 2003. The invasion removed Saddam Hussein but was followed by occupation, insurgency, and sectarian violence. Claims about Iraqi weapons of mass destruction used to justify the war were not substantiated by the subsequent searches.

Rumsfeld faced criticism over troop numbers, planning for the occupation, equipment shortages, and policies affecting detainee treatment. The Abu Ghraib abuse scandal intensified scrutiny of command responsibility and interrogation practices. Disputes with military officers and members of Congress grew as the Iraq conflict worsened. Bush announced his replacement after the 2006 midterm elections, and he left office in December. Rumsfeld later published memoirs and participated in charitable work before his death in 2021. His career combined legislative experience, senior executive administration, and business leadership, but its most consequential legacy concerns the organization and conduct of the post-2001 wars. Assessing it requires attention both to the initial military successes and to the assumptions, decisions, and oversight failures that contributed to prolonged conflict.