Final answer:
The Red Scare attitude in 1920 was revived by the fear of a leftist revolution or communist takeover, which was intensified by the trial of Italian immigrants, Sacco and Vanzetti.
Step-by-step explanation:
The event that revived the Red Scare attitude in 1920 was the fear of a leftist revolution or communist takeover, similar to what occurred in Russia in 1917. This fear was intensified by the trial of Italian immigrants, Sacco and Vanzetti, who were seen as symbols of foreign radicalism. The Red Scare was a period of increased fear and paranoia regarding the potential threats posed by anarchism and communism.