First, I assume that virtually all of the 12 thousand Hoover wished to arrest in the Summer of 1950 were CPUSA members or regarded by the FBI as "fellow travelers" (in the jargon used by red-baiters at the time). Weiner mentions they were part of an existing index. Actually, it is important to note Hoover had been compiling such a list for many years, and, when ordered by New Deal Attorney General Francis Biddle to end it during WWII, told Biddle that he did, hid it under another label, and continued it. Even during WWII, the list, which eventually numbered hundreds of thousands, was comprised overwhelmingly of Communists and other leftists whom the bureau regarded as "fellow travelers."
In September 1950, Congress passed the McCarran Internal Security Act, whose key sponsor was the right-wing Nevada Democratic Senator, Pat McCarran, whom some, myself included, believe was the role model for the corrupt Nevada Senator in the classic U.S. film, The Godfather II. The Act was essentially a reworking of the right-wing Republican sponsored Mundt-Nixon bill, which had crashed and burned in 1948. Along with establishing a "Subversive Activities Control Board" to list, search, and destroy mass organizations that it declared to be "Communist fronts," The McCarran Act called for the establishment of what were political detention camps (its opponents called them concentration camps) in the event of a "national emergency," that is, mass arrests and imprisonment. This was not carried out but which remained a serious threat at a time when the national leadership of the CPUSA had already been convicted in a political show trial under the Smith Act, state and local leaders of the CPUSA were soon to be brought to trial,and cold warriors were calling for a great extension of these purge trials (the attack on civil liberties was so extensive that some "liberals" were taking the position that the arrests and trials should be continued against CPUSA leaders, but not members).
It is also important for our readers to remember that what J. Edgar Hoover wanted authorization for in July, 1950, the mass arrest without habeas corpus and imprisonment of thousands of Communists and their allies, he had accomplished as a young attorney and head of the General Intelligence Division of the Justice Department when he convinced the Attorney General, A. Mitchell Palmer, to approve of mass arrests, imprisonment, and deportation of "alien radicals" whom he linked to Bolshevik conspiracies in early 1920.
These "Palmer raids" resulted in the arrest of 10,000 people (the majority of whom were U.S. citizens) and the eventual deportation of hundreds to what was then Soviet Russia, including the anarchist Emma Goldman, who never was permitted to return to the U.S. in spite of her subsequent writings which were very critical of the Soviets. In 1919-1920, Hoover spread stories of Bolshevik conspiracies to launch a Soviet style revolution in the U.S. in order to intensify the postwar Red Scare which targeted trade unionists and African-American veterans returning from WWI. Hoover used the wild stories of Bolshevik conspiracies to bomb government installations and assassinate leaders to win support for his plans for mass arrests and deportations.
Hoover became director of the FBI in 1924 (appointed ironically by a new Attorney General and later progressive Supreme Court Justice, Harlan Fiske Stone, who had opposed the then discredited Palmer Raids but didn't know that Hoover was behind them)and essentially created the FBI in his own twisted image as a political police force, holding the position of director until his death in 1972. After WWII, Hoover fed his friends in the press and friendly politicians like Richard Nixon and Joe McCarthy stories of Communists acting as Soviet spies in and outside of government to both expand his power and also to the arrest and imprisonment without constitutional rights of the people who were on his ever expanding lists (the espionage theme had much more oomph after WWII than mad Bolshevik bombers, assassins, and rioters that he he had used in the post WWI Red Scare.
Tim Weiner concluded his story by saying that neither Truman or any other president approved Hoover's plans. While that is true Hoover usually worked without the specific knowledge of Attorneys General and Presidents when he had to, always seeking to create a climate of fear to sustain his activities. The left generally and the CPUSA particularly were his major targets from WWI to the late 1960s, when he made the Black Panther Party his number one target and in alliance with federal, state, and local political elites and law enforcement agencies launched a campaign to destroy the BPP by fomenting terroristic violence against it and arresting its leadership on a variety of usually trumped up criminal charges.
The Bush administration has used the Patriot Act to continue what was J. Edgar's life work, proclaiming its right to do openly what he most of the time had to do covertly, although he tried to get presidential and congressional approval for his acts, as this document shows. This history is important to remember, both in understanding Hoover's 1950 overture to Truman and the present policies of the Bush administration, since the Bill of Rights is not now nor has it ever been a given in U.S. history. Constitutional Rights, including elemental rights of habeas corpus, protection against warrantless searches and seizures, cruel and unusual punishments, have to be won and won over and over again from the predatory politicians and police agents for whom they are barrier to protecting their power and the interests of the exploiting classes which they serve.