McCarthyism is a political practice defined by the accusation and investigation of left-wing individuals of communist and Soviet influence on American institutions and of Soviet espionage in the United States during the late 1940s through the 1950s, heavily associated with the McCarthy era. After the mid-1950s, U.S. senator Joseph McCarthy, who had spearheaded the campaign, gradually lost his public popularity after several of his accusations were found to be false. The U.S. Supreme Court under Chief Justice Earl Warren made a series of rulings on civil and political rights that overturned several key laws and legislative directives, and helped bring an end to the Second Red Scare.