McCarthyism is a political practice defined by the political repression and persecution of left-wing individuals and a campaign spreading fear 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 Second Red Scare, also known as the McCarthy era. After the mid-1950s, U.S. senator Joseph McCarthy, who had spearheaded the campaign, gradually lost his public popularity and credibility 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.
Historians have suggested since the 1980s that as McCarthy's involvement was less central than that of others, a different and more accurate term should be used instead that more accurately conveys the breadth of the phenomenon, and that the term McCarthyism is, in the modern day, outdated. Ellen Schrecker has suggested that Hooverism, after FBI head J. Edgar Hoover, is more appropriate. Following the end of the Cold War, unearthed documents revealed substantial Soviet spy activity in the United States, although many of the agents were never properly identified by McCarthy.