Final answer:
The author of the statement about Communists in the State Department is Senator Joseph McCarthy, who led a campaign of accusing government officials without proper evidence in the 1950s.
Step-by-step explanation:
The author of the statement, "In my opinion the State Department, which is one of the most important government departments, is thoroughly infested with Communists. I have in my hand 57 cases of individuals who would appear to be either card carrying members or certainly loyal to the Communist Party, but who nevertheless are still helping to shape our foreign policy," is Joseph McCarthy. This statement is closely associated with Senator McCarthy's crusade against alleged Communists within the U.S. government during the early 1950s, specifically within the State Department, which was a significant focus of his anti-Communist campaign. As history records, McCarthy's claims were often unsubstantiated, and his tactics came to be known as 'McCarthyism,' referring to the practice of making accusations of disloyalty, subversion, or treason without proper regard for evidence.