The Naked Communist - W. Cleon Skousen (pub. 1958, 1960, 1961)

Eugene McCarthy was over-zealous but he wasn't crazy. Apparently, for many years, several Americans really were spying for the Russians. This book discusses the Marxist roots of communism, beliefs and theories, Russian history, and to a lesser extent, Cuban history. The writing style is a little paranoid, which would be expected as this book was written during the cold war.