Final answer:
The correct answer is option 4. The era of McCarthyism was marked by the use of false accusations of communism against political opponents without providing evidence, creating an atmosphere of fear that suppressed public discourse and civil liberties.
Step-by-step explanation:
The political trend that characterized the era of McCarthyism was the use of false accusations of communism as a weapon against political opponents. Senator Joseph McCarthy, a Republican from Wisconsin, initiated a series of actions in the early 1950s that became synonymous with McCarthyism.
This term now refers to the anti-Communist hysteria of the postwar period and McCarthy's technique of issuing unsustantiated accusations of disloyalty without providing evidence. During this time, the atmosphere of fear and paranoia led to many Americans being hesitant to speak out on any public issues for fear of being labeled as communists, significantly affecting civil liberties and political discourse.