Over the course of history, a small percentage of Jews became out and out communists. That does not mean that Jews were not paramount in the movement, because the Communist party never had a large number of adherents in the US--just powerful ones. It just means that idealistic and somewhat alienated immigrants from a tradition and culture that was more collectivist and urban were more prone to identify with an ideology that had as its aim the replacement of American democracy with something else. I don't condemn them too much for their views, it developed out of a naive brand of concern for the social welfare that was admirable. However, once the crimes of Stalin became known, you could not excuse those who identified with the communists. By the late 1930s, communists were no longer idealists, but wannabe tyrants, people who wanted to tear down the US and run it themselves as a dictatorship.
In any event, Christians bought into it, too, but in percentage terms, Jews were much more likely to be involved in communist politics, and a much higher percent of the Communist movement than other ethnic groups.
Thanks for the explanation. At first glance, it appeared that your comment was saying Jewish=Communist.