Did Communism Threaten America's Internal Security After World War II?

I agree with historians John Earl Haynes and Harvey Klehr that communism did threaten American security after World War II. As uncovered by the messages decoded by the Venona Project's "code-breakers," there were hundreds of Communists in America who served as spies to the Soviet Union in the 1940's and 50's. Spies ranged from scientists to high government officials, and most were members of the American Communist Party. They uncovered domestic, military, and atomic secrets to the Soviet Union. Due to the espionage of scientists Klaus Fuchs, Theodore Hall, and David Greenglass, the Soviets were able to develop the atomic bomb years earlier and at a much lower cost than they would have been able to without that classified information. While people like Senator McCarthy took their "red hunt" too far, Communism, especially involving espionage, was a serious threat to American security after World War II.