Lyndon B. Johnson's tenure as the 36th president of the United States began on November 22, 1963, upon the assassination of president John F. Kennedy, and ended on January 20, 1969. He had been vice president for 1,036 days when he succeeded to the presidency. Johnson, a Democrat from Texas, ran for and won a full four-year term in the 1964 presidential election, in which he defeated Republican nominee Barry Goldwater in a landslide. Johnson did not run for a second full term in the 1968 presidential election because of his low popularity. He was succeeded by Republican Richard Nixon. His presidency marked the high tide of modern liberalism in the 20th century United States.

Modern liberalism in the United States is based on the combined ideas of civil liberty and equality with support for social justice. It is one of two major political ideologies of the United States. Economically, modern liberalism supports government regulation on private industry, opposes corporate monopolies, and supports labor rights. Its fiscal policy opposes any reduction in spending on the social safety net, while simultaneously promoting income-proportional tax reform policies to reduce deficits. It calls for active government involvement in other social and economic matters such as: reducing economic inequality, increasing diversity, expanding access to education and healthcare, regulating economic activity, and environmentalism. Modern liberalism is a large and mainstream ideology in the Democratic Party and nation. Modern liberalism was formed in the 20th century in response to the Great Depression. Major examples of modern liberal policy programs include the New Deal, the Fair Deal, the New Frontier, the Great Society, the Affordable Care Act, and the Infrastructure Investment and Jobs Act.