Revelations that spies in the US atomic program had passed secrets to the Soviet Union set off a nationwide panic that communist spies might be infiltrating many American institutions.
Allegations that Hollywood was rife with communists led the House Committee on Un-American Activities (HUAC) to investigate many actors, writers, and directors during the 1950s. Alleged communists were placed on a blacklist and barred from working in Hollywood.
Republican Senator Joseph McCarthy took advantage of this widespread paranoia to advance himself politically by accusing State Department employees of communist leanings. McCarthy's accusations were unsubstantiated, and the Senate eventually censured him.