Nobody believed the Bush spin about why Miers withdrew, so how effective a cover was it? That nomination was going down whether Krauthammer said a word or not.
True, the nomination was going down, but in order for the President to retain control of the process, HM had to withdraw for at least semi-plausible reasons. Krauthammer (and no one else, I might add, until later) provided that. Fred Barnes lamented that since Krauthammer said this brilliant plan publicly, it would be unable to be implemented. Regardless, it was a plan of action, and we got Alito instead of Miers. A good day's work, indeed.