During the 1920s and 1930s, there were a lot of socialists in the United States. Remember, at the time, this was before the Soviet Union was our enemy and just after the 1917 Revolution in which socialism was still perceived to be a "noble experiment" and not yet proven to be the failure we all know it is today.
Huey Long, who served as governor of Louisiana and also U.S. senator was a radical socialist who was becoming wildly popular throughout the country. He wanted to become president of the United States and abolish capitalism and confiscate the wealth of the nation's rich and redistribute it. He even wrote a book about it called My First Days In The White House. We're talking about a guy who thought FDR was a radical conservative and a puppet of Wall Street! Had he not been shot, who knows what might have happened.
Huey Long was assassinated in 1935 while he was running for president for the 1936 campaign. The United States came perilously close to being a socialist country during that time.
Well...yes and mostly no. Long was probably more along the lines of a fascist (although I think he was just an opportunist). After Long's death, his "cause" was taken up by Gerald L.K. Smith, definitely a fascist. Anyway, for more on the FASCINATING material on the subject of Huey Long, I would recommend T. Harry Williams' Huey Long, probably the most interesting book about a politician ever written. He sort of innovated the interview type of biography where much of the book was based on people who knew Long.