Betcha It Was Specter

"This is the most incompetent White House I've seen since I came to Washington. The White House legislative liaison team is incompetent, pitiful, embarrassing. My colleagues can't even tell you who the White House Senate liaison is. There is rank incompetence throughout the government. It's the weakest Cabinet I've seen."

-An anonymous GOP Senator quoted by David Ignatius of The Washington Post

It had to be a GOP Senator who has been around a while, so my money is on one of the following (all have served through four full administrations counting Bush);

Ted Stevens (R-Alaska)
Pete Domeninci (R-New Mexico)
Richard Lugar (R-Indiana)
Orrin Hatch (R-Utah)
Thad Cochran (R-Mississippi)
Chuck Grassley (R-Iowa)
Arlen Specter (R-Pennsylvania)

Of them, my guess would be Specter. I'd be interested to find out if I was right though