We lowered our long-term rating on the U.S. because we believe that the prolonged controversy over raising the statutory debt ceiling and the related fiscal policy debate indicate that further near-term progress containing the growth in public spending, especially on entitlements, or on reaching an agreement on raising revenues is less likely than we previously assumed and will remain a contentious and fitful process. We also believe that the fiscal consolidation plan that Congress and the Administration agreed to this week falls short of the amount that we believe is necessary to stabilize the general government debt burden by the middle of the decade.
Republicans and Democrats have only been able to agree to relatively modest savings on discretionary spending while delegating to the Select Committee decisions on more comprehensive measures. It appears that for now, new revenues have dropped down on the menu of policy options. In addition, the plan envisions only minor policy changes on Medicare and little change in other entitlements, the containment of which we and most other independent observers regard as key to long-term fiscal sustainability.
http://blogs.wsj.com/marketbeat/2011/08/05/sp-downgrades-u-s-debt-rating-press-release/