Jews were/are highly overrepresented in the leadership and rank of file of Left orgs. historically.
See , "Jews and the Left, " a big book on this by Arthur Liebman.
Also Jack Salzman and Cornel West anthology on Blacks and Jews, and , "Jewish Radicalism, " ed. by Jack Nusan Porter and Peter Dreier.
Almost forgot this one. The chapters on the Vietnam War, the New Left and Israel are very good.Torn at the Roots: The Crisis of Jewish Liberalism in Postwar America" written by Michael E. Staub - Columbia University Press, 2002. Excerpt here, http://pnews.org/PhpWiki/index.php/LimitsOfJewishDissent
http://www.axt.org.uk/HateMusic/essay_cohen_delegitimisation.htm A DISCOURSE OF DELEGITIMISATION: THE BRITISH LEFT AND THE JEWS
-- Michael Pugliese