Who was Joseph McCarthy, and what did he do?
He was a senator from Wisconsin. To help get elected, he claimed he know of 205 USSR spies working in the state department. Most of the public believed him. Between 1950 and 1954, he claimed many Americans were spies, and got them arrested. Finally in 1954, everyone realized that he made up or exaggerated a lot of accusations, and he was banned from the senate.