The latest technique used by conservatives to silence liberal academics is to demand copies of e-mails and other documents. Attorney General Kenneth Cuccinelli of Virginia tried it last year with a climate-change scientist, and now the Wisconsin Republican Party is doing it to a distinguished historian who dared to criticize the state’s new union-busting law. These demands not only abuse academic freedom, but make the instigators look like petty and medieval inquisitors.

The historian, William Cronon, is the Frederick Jackson Turner and Vilas research professor of history, geography and environmental studies at the University of Wisconsin, and was recently elected president of the American Historical Association. Earlier this month, he was asked to write an Op-Ed article for The Times on the historical context of Gov. Scott Walker’s effort to strip public-employee unions of bargaining rights. While researching the subject, he posted on his blog several critical observations about the powerful network of conservatives working to undermine union rights and disenfranchise Democratic voters in many states.

In particular, he pointed to the American Legislative Exchange Council, a conservative group backed by business interests that circulates draft legislation in every state capital, much of it similar to the Wisconsin law, and all of it unmatched by the left. Two days later, the state Republican Party filed a freedom-of-information request with the university, demanding all of his e-mails containing the words “Republican,” “Scott Walker,” “union,” “rally,” and other such incendiary terms. (The Op-Ed article appeared five days after that.)

The party refuses to say why it wants the messages; Mr. Cronon believes it is hoping to find that he is supporting the recall of Republican state senators, which would be against university policy and which he denies. This is a clear attempt to punish a critic and make other academics think twice before using the freedom of the American university to conduct legitimate research.