Which action of Joseph McCarthy contributed to increased cold war anxieties?

Answer 1

His 'Red Scare" policy in which he accused people left and right (but mostly 'left') of being Communist sympathizers. Although he almost never produced a single scrap of hard evidence, he browbeated people in either confessing to having Communist - also meaning 'Socialist', or just liberal - leanings, or he threatened to 'expose' them unless they named others.

Although he had been accusing political rivals and basically anyone who crossed him of being Communists for all his adult life, he now had world events giving him some credibility: the recent installing by the USSR of Communist regimes in eastern Europe, plus several cases of USSR espionage in the US, especially in the field of US atom bomb technology. And he had an eager supporter of his Communist witch hunt: the FBI's J. Edgar Hoover.

When he started to also accuse hundreds of public servants of being 'secret' Communists and - even worse in the eyes of his fellow Senators - promised to 'expose' members of US Congress as Communists, his fellow Senators finally stepped in. In an official report by the US Congress it was shown that he had in almost all cases persecuted people for no good reason and without any proof. It proved to be the end of McCarthy's career.