How did America react to China's conversion to Communism?

China didn't exactly just convert to communism. In 1949, Mao's communist forces successfully routed the nationalist forces of Chiang Kai Shek, whose government left for Taiwan. The United States continued to recognize the Taiwan-based government as the legitimate government of China until Nixon opened up relations with Beijing in the 1970's. Carter subsequently switched official recognition of China from Taipei to Beijing.