It isn't clear how much Marx that Reagan might actually have read, but judging by what little he said and the depth of Marxist knowledge by Reagan's supporters here, it probably wasn't much more than "The Communist Manifesto" (1848). The reason that this is important, is that most of Marx's volumes of writings are on a criticism of socio-economic implications of class relationships under capitalism, and "The Communist Manifesto", while not unimportant, is essentially a pamphlet. Most of Marx's writing is philosophy and criticism. To characterize Marx simply as one of the creators of the idea of Communism is to broadcast your ignorance about Marx's work. To say you understand Communism and Marx by reading "The Communist Manifesto" is like saying you understand Christianity solely based on the song, "Silent Night".