The problem of balancing the internal national security of the United States with the civil liberties of its citizens has ebbed and flowed over the past 50 years. Congressional legislation often linger longer than the passions that push the passage of the legislation. The McCarran Act of 1950, passed in the aftermath of revealed Communist espionage and the onset of the Korean War, had a profound impact on internal security long after anti-Communist passions had cooled. This study examines the McCarran Act of 1950 and argues that Supreme Court decisions in cases involving the McCarran Act and other anti-Communist legislation created a framework within which Congress created future internal security legislation, including the USA Patriot Act of 2001. This work is directed towards historians of Anti-Communism and researchers interested in internal security legislation.