Let us call it what it is...
The Republican Downgrade
The political brinksmanship of recent months highlights what we see as America’s governance and policymaking becoming less stable, less effective, and less predictable than what we previously believed. The statutory debt ceiling and the threat of default have become political bargaining chips in the debate over fiscal policy ... It appears that for now, new revenues have dropped down on the menu of policy options.
Compared with previous projections, our revised base case scenario now assumes that the 2001 and 2003 tax cuts, due to expire by the end of 2012, remain in place. We have changed our assumption on this because the majority of Republicans in Congress continue to resist any measure that would raise revenues, a position we believe Congress reinforced by passing the act.
It seems that the S&P is saying this is due specifically to the Republicans being unwilling to compromise and because the Democrats are too weak to do anything to actually help the economy revenue side.
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.
Basically, the S&P sounds like they have been reading Dailykos.