And while Moody's and Fitch, the other leading rating agencies, have affirmed the top rating, they too have worried about the long-term prospects for the United States.
None of this necessarily means disaster for your money. The United States has not been downgraded to "junk" status, like say, Greece. The rating is still very high -- just not tops.
Still, there could be ripple effects. Here's where.
Skittish investors who wouldn't want to park their cash in downgraded Treasuries might feel more secure by putting that money into an FDIC-backed bank account instead, since it would be protected by deposit insurance, says FPA New Income manager Thomas Atteberry.
But the increased sense of security would be little more than psychological, says Peter Crane, president of Crane Data, which tracks the money-market fund industry; after all, like Treasuries, FDIC-insured accounts are ultimately backed by the same entity: the U.S. government.