His professors at Columbia included Harry Carman, Henry Steele Commager, and David Donald. But it was Columbia historian Richard Hofstadter's "The American Political Tradition" that made the most lasting impression. Zinn regularly included it in his lists of recommended readings, and, after Barack Obama was elected President of the United States, Zinn wrote, "If Richard Hofstadter were adding to his book "The American Political Tradition", in which he found both 'conservative' and 'liberal' Presidents, both Democrats and Republicans, maintaining for dear life the two critical characteristics of the American system, nationalism and capitalism, Obama would fit the pattern."