In reality, the Communist party isn't really a threat, especially in the United States. Communism is simply another political and social view in comparison to Republicans and Democrats. Banning the Communist party would bring us back to the days of McCarthyism, which is something that this country doesn't need again.
The communist party or parties pose no greater threat to our country than any other third political parties,such as the Libertarian or Green. While it presents a method of running a country that is very different from capitalism, it is a real choice that the American voters have a right to accept or reject.