By the 1960s [J. Edgar] Hoover had become one of the most powerful political figures in America, thanks chiefly to his ability to use the FBI's notorious Division Five (successively named the National Defense Division, the Security Division, and the Domestic Intelligence Division) to intimidate, blackmail, or destroy the careers of people who were not accused of any crime, but whom he deemed to be dangerous.

Hoover had first exercised such powers during the Red Scare of 1919, when, as head of the Justice Department's General Intelligence Division, he had without trial deported hundreds of aliens (along with Emma Goldman, who was arguably an American citizen) in the so-called Palmer Raids. Hoover had acted at times without consulting or informing President Wilson, in collaboration with a huge army of volunteer spies, the American Protective League, which had been organized by business executives. Hoover did not by any means act alone; to help put down a national steel-industry strike at this time, the U.S. Army imposed martial law in certain areas.

One should acknowledge that Hoover himself briefly played a different role, professionalizing the Bureau of Investigation, and accepting for about a decade the directive given him by Attorney General Harlan Stone on May 13, 1924: "The activities of the Bureau are to be limited strictly to investigations of violations of law." Although he had been a major player in the Palmer Raids of 1919–1920, Hoover now (for over a decade) dismantled his General Intelligence Division, concentrated on solving personal crimes already committed, such as bank robberies, and never again involved the Bureau in anything like the Palmer Raids.