Sean Wilentz is a Princeton historian of great vigor and ability. He has published a number of scholarly books on American history. He is a liberal activist, and a friend of the Clintons. For some Obama champions, his recent enthusiasm for Hillary Clinton passed from acceptable to treacherous: He did not simply back Clinton, he stabbed Barack Obama in the back. In this article, the author discusses how Wilentz' attack on Obama reveals something important about intellectual contestation today. Many critics like Wilentz improperly conflates two roles--professional historian and public commentator--when they write stuff about people, issues, and events. Their points are well taken but also misleading to people who read their writings.