Threshold Editions, part of Simon & Schuster, announced today that conservative radio host and author Mark R. Levin’s “Liberty and Tyranny: A Conservative Manifesto” has officially sold one million copies since its release in March. No thanks to the mainstream media.

As the Culture and Media Institute detailed in a new Special Report “Unmentionable: Best Selling Conservative Books and the Networks that Ignore Them,” Levin’s book, which spent 12 weeks at No. 1 on the New York Times Best Sellers List, has been ignored by the mainstream media. Levin told CMI that “we have not heard from any of the major networks, and the only major newspaper that has interviewed me is Philadelphia Inquirer, and that’s because I’m from Philadelphia.”

Obviously, that hasn’t harmed sales. “The book is selling by word of mouth,” Levin said. “I’ve done very little media, and its chugging along.”

Levin hasn’t been the only conservative author getting the cold shoulder from the MSM. The CMI Special Report found that in the first half of 2009, the three broadcast networks covered liberal bestsellers three times as often as comparable conservative titles. Of the 11 conservative authors on the list, just four received any coverage on the networks. On the other hand, the networks covered 11 out of 14 liberal authors.

Furthermore, when authors appeared on the networks for interviews, conservatives received markedly different treatment than liberals. From Matt Lauer calling Elizabeth Edwards’ book “stirring,” to Harry Smith telling Ann Coulter, “You have this kind of sophomoric sort of simplistic kind of view of so many things,” hosts made it clear where their ideological sympathies lay.