Here’s the problem: Credit rating companies have long contended that their conclusions are protected by the First Amendment, much as if their ratings were as irrelevant to the markets as, say, your average financial column. Dodd-Frank tried to change that, designating the agencies “experts,” just like lawyers or accountants, when their ratings were included in S.E.C. documents for certain kinds of offerings. That would make them liable for material errors and omissions in their ratings.