From what I understand, the downgrade is largely due to Congress' unwillingness to consider any form of increases to tax revenue, even as a last resort to avoid default. The fact that the House couldn't pass an already-weak compromise bill simply because it increased revenues is worrisome for our creditors.
On a side note:
This whole Tea Party thing is just daft, when the original tea party was about taxation without representation. The founding fathers were all for taxation to pay government debt, just not taxation to line the pockets of King George. After the revolutionary war, there were huge war debts to pay off. How did they do it? Monetary policy and taxation, just like every government until Bush 43, and that includes Reagan and Bush 41. How did we get out of the Great Depression? Government spending on public works and heavy industry to support our allies in the run-up to WW2.
But I guess that's what happens when you slash education spending: people don't know things.