The "independent" ethics adviser that astroturf lobbyist Jack Bonner told Congress he'd retained in the wake of the flap over those forged letters to lawmakers has backed out of the role, citing the TPMmuckraker-driven fallout over an ad he placed this week praising Bonner.

James Thurber, a long-time political science professor at American University, told National Journal he'll recommend a different ethics adviser for Bonner's firm, and noted:

I teach a class on ethics and lobbying and I have never had anything like this. There have been articles about this and I have received phone calls. I never am going to do [ads] like this again, thanking people. I'll do it through personal correspondence.

Thurber had planned to do the job pro bono.

Earlier this week, TPMmuckraker reported on an ad placed in Roll Call by Thurber's Center for Congressional and Presidential Studies, which thanked Bonner for "over 15 years of teaching excellence." As we wrote, Bonner has long been a part-time instructor for Thurber's program -- just last weekend he taught a workshop on "the art and craft of lobbying" -- and a decade ago, the two collaborated on a study of congressional use of the internet.

The ad -- which National Journal reports cost $1,523 -- and the history of ties between the two men raised questions as to whether Thurber could act as the truly independent adviser that Bonner had promised Congress he would bring in. That promise was one of several steps Bonner announced he was taking after his firm, working on behalf of a coal-industry client, sent out forged letters urging lawmakers to vote against climate change legislation. The letters purported to come from local community groups.

A Bonner spokesman on Wednesday defended the decision to turn to Thurber, telling TPMmuckraker that the professor was "above reproach," and that hiring an adviser from an outside law firm would have been costlier and more time-consuming.

American University has told TPMmuckraker it is probing the circumstances surrounding the ad.