Why was joseph mccarthy so powerful during the 1950s, and what factors led to his decline?

Joseph McCarthy gained significant political power during the 1950's due to his claims of knowing about communists in American society. After World War II, the United States was fearful of the spread of communism as the Soviet Union emerged from this war as a global superpower. Considering this factor, McCarthy's accusations lead to increased suspicion in American society. His claims fueled American's worst fears.

 Initially, he was seen as an American patriot who was trying to rid America of communist influence. His power was then fueled by the hearings of the House Un-American Activities Committee, where people with supposed communists ties were called before Congress to testify.

However, McCarthy's power declined after failing to prove many of his claims. Along with this, his accusations that the US military and some of their highest ranking officers were communist, lead to the American citizens to turn on him.