The term Red Scare has cropped up recently in discussions here, but in a way to suggest that Communism in America has never been a real threat. I used to believe this myself.
There were two Red Scare periods in America. The first, which roughly corresponded with the Bolshevik Revolution and WWI, was associated with the international labor movement and was inspired by strikes, riots and bombings that understandably frightened the public. The second is associated with McCarthyism, but while there were elements of political hysteria, the basic claims of Soviet/Communist infiltration of the U.S. government and other institutions were ultimately confirmed.
Communists and their supporters have been active in American politics for more than 100 years. To suggest their influence has been benign is factually incorrect.