At this point, most everyone has heard that S&P downgraded U.S. government debt on Friday. An important piece of the story involves the $2.1 trillion error in debt that S&P provided in its original rationale. As one might expect, officials are using the error and S&P’s earlier failure to properly rate bundled mortgage products to argue that the downgrade is incorrect. S&P’s reputation, whether the downgrade is correct or not, is sure to take a hit.