There are two main pieces of "information" that McCarthy gives to show that the US was losing the war against communism.
First, McCarthy gave numbers for how many people lived under communist domination in 1944 and 1950, respectively. He said that the number went from 180 million to 800 million in those years.
Second, McCarthy cited some specific examples of people who he said were communists and were working in the State Department. He also claimed to have a list of other people that he did not name who were communists or were helping the communists while working for the State Department. McCarthy cited this "information" to show how it was possible for the US to be losing in the Cold War.
Wisconsin Republican Senator Joseph McCarthy made a famous speech at Wheeling, West Virginia, on February 9, 1950, that many regard as the starting point of McCarthyism, the often unconstitutional crackdown that McCarthy led on anyone he deemed politically subversive (or anyone who opposed him). In his speech, he said the following:
"Six years ago, . . . there was within the Soviet orbit, 180,000,000 people. Lined up on the antitotalitarian side there were in the world at that time, roughly 1,625,000,000 people. Today, only six years later, there are 800,000,000 people under the absolute domination of Soviet Russia—an increase of over 400 percent. On our side, the figure has shrunk to around 500,000,000."
The evidence he uses to support his idea that Communism is emerging victorious over America is that the number of people controlled by the Soviets, though their takeover of satellite states, has grown exponentially in the last six years (since the end of World War II). At the same time, the number of people on the anti-communist side is shrinking. He plants in the audience's mind the idea of the "communist menace" that is taking over the globe. In the weeks before his speech, China had become a Communist country, and the Soviets had detonated an atomic bomb, increasing Americans' fears about the spread of Communism.
At the end of the speech, he states that there are 205 people in the State Department who are known Communists but are still permitted to work there. Two days later, on February 11, he stated that there were 57 Communists in the State Department, a claim denied by President Truman but one that set off a great deal of national hysteria.