From S&P’s historic downgrade of the US credit rating on August 5, 2011:
More broadly, the downgrade reflects our view that the effectiveness, stability, and predictability of American policymaking and political institutions have weakened at a time of ongoing fiscal and economic challenges to a degree more than we envisioned when we assigned a negative outlook to the rating on April 18, 2011.
Read more at Here's A Disturbingly Astute Line From When S&P Downgraded The US Credit Rating | Business Insider Australia.