In this context, "McCarthyism" referred to an attitude or behavior, while Jedgar was a person (who looked quite good in a LBD, BTW).
Jedgar practiced McCarthyism so much that he became one of its embodiments, even long before the Truman-McCarthy era, but not all of those who practice McCarthyism end up that way, because they grow up, become more broad-minded, willing to think for themselves, etc.
(BTW, have people seen or heard the musical "J. Edgar!," co-authored by Harry Shearer? Fun.)
Jim Devine "Segui il tuo corso, e lascia dir le genti." (Go your own way and let people talk.) -- Karl, paraphrasing Dante.