A few people are to blame here
1) S&P for that awful calculation error
2) House Republicans for refusing to let the tax cuts expire
3) George W Bush for invading Iraq
4) Whoever the hell had the stupid idea of separating debt ceiling votes from the Budget (the S&P report mentioned this)
I'm trying to fault the Democrats at least slightly, but I can't. They were excessively resistant to cuts, but nowhere near as bad as the Republicans with regards to tax increases.