"The problem, however, is that any attempt to sue the credit rating agencies for downgrading U.S. securities will run smack into the Bill of Rights. The rating agencies, as many a disgruntled mortgage-backed securities investor has discovered in the last few years, are shielded from liability because their ratings are considered to be public opinion protected by the First Amendment of the U.S. Constitution."
(hyperlinks embedded in Reuters article)
http://blogs.reuters.com/alison-frankel/2011/08/02/angry-about-possible-u-s-downgrade-dont-bother-suing-raters/and - just as pertinent concerning the MBS misratings:
"The First Amendment shield has proved to be incredibly valuable to the credit rating agencies in the wake of the 2008 economic meltdown, when court after court has dismissed MBS investors’ claims that the rating agencies worked hand-in-glove with issuers to confer AAA ratings on mortgage-backed dreck."
Don't blame Holder or Obama - the courts have decided (for now).
Good news? Dodd-Frank attempts to remove this immunity. But the CRA's are fighting it, of course.