Stephen Spruiell explains that stimulus spending has become an unfalsifiable religion.
Brian, you left out my favorite part of that CBO report: "Economic output and employment in the spring and summer of 2009 were lower than CBO had projected at the beginning of the year. But in CBO’s judgment, that outcome reflects greater-than-projected weakness in the underlying economy rather than lower-than-expected effects of [the stimulus]."
The case that the stimulus is working is thus rendered non-falsifiable. Its supporters will always claim that it is working fine, but we can't see it, because the "underlying" economy (whatever that is) is so much worse than anticipated. Belief in its efficacy is a faith, at odds with sound economics.
Well, it's religion or politics: after spending so much money, it simply can't be allowed to be perceived to have failed.