Good article in Time: Why Standard & Poor's and Congress Deserve Each Other

Having Standard & Poors downgrade the creditworthiness of the United States, and warn it about further downgrades, is a little like having the Catholic Church lecture scout leaders on the proper behavior toward boys. The moral authority seems to be wanting. S&P, you may recall, is one of the ratings agencies, the others being Moody's and Fitch, that greased the skids of the financial crisis by awarding AAA ratings to tranche after tranche of mortgage bonds called collaterized debt obligations, or CDOs. Recall that, unlike U.S. Treasuries, backed by the full faith and credit of the United States, CDOs were underwritten by garbage mortgages - that is, backed by no documentation "liar loans," and other Alt A subprime pond scum handed to borrowers who otherwise couldn't get a nickel's worth of credit at their local dry cleaners.