Freedom became a national horizon
Freedom is the very idea on which the USA were founded. It guided Americans during their entire history despite the numerous limits, like the treatment of Native Americans or African Americans.
Freedom was used as a pretext to justify the numerous military interventions for instance in Vietnam or in Europe during world wars.
MLK referred to the American declaration of indepence during his "i have a dream" speech during the March on Washington.(28th August 1963). These ideals remained vibrant in American political life.