Leaked emails show that conservative historian Niall Ferguson conspired with two conservative Stanford University students to run an "intimidation" campaign against campus progressives that even included "oppo research" on a progressive student.

Stanford Daily reports that Ferguson, a former Harvard professor who is now a fellow at the Stanford University-based Hoover Institute think tank, encouraged conservative activists John Rice-Cameron and Max Minshull to dig up opposition research on progressive activist Michael Ocon.

"Some opposition research on Mr. O might also be worthwhile," Ferguson wrote to the two young Republicans. Minshull replied to Ferguson that he would "get on the opposition research" against his fellow Stanford classmate.

In other emails, Ferguson spoke of "grinding down" their opponents, while recommending actions that he said would "intimidate" them.

The emails were written in reaction to protests against the Stanford "Cardinal Conversations" program's invitation of Charles Murray, who in the past has drawn heavily criticized and widely debunked links between race and IQ scores, to speak at the school.

Ferguson has since resigned from his leadership role at the Cardinal Conversations program and has apologized for the "inflammatory" tone of his emails.

“It seemed to me that the Cardinal Conversations student steering committee was in danger of being taken over by elements that were fundamentally hostile to free speech,” he wrote to The Daily. “It was, however, rash of me to seek to involve the Stanford Republicans, and reckless to use such inflammatory language.”