Tyler Cowen has six useful thoughts here. I’d add a few more:

1) S&P is downgrading their estimation of our political system, not our actual ability to pay our debts. Indeed, the past 36 hours offered a stunning demonstration of the market’s faith in our ability to pay our debts. The panic sent investors rushing to buy Treasuries, sending yields on 10-year Treasuries to 2.4 percent -- that’s almost nothing -- and demonstrating that American debt is still considered the safest bet in the world. That vote of confidence under real world conditions is far more important than anything S&P says.

2) Of course S&P is downgrading our political system. Did you see the nonsense we pulled over the past few months? The Republican Party took the country to the brink of default, and for what? A smaller and less certain deficit-reduction deal than they could have gotten if they had been willing to compromise with the Democrats. And then Senate Minority Leader Mitch McConnell said these default-driven deals would be the norm around Washington from now on. Why shouldn’t S&P downgrade our debt? Read on...