The tendency to attribute outright magical powers to government spending has gotten slightly out of control. It's appropriate to ask the same question that should have been asked of Republicans in 1980: if all this is so marvelous, why don't we just do it indefinitely--slash tax rates to zero, borrow and spend forever?

The answer is that there are declining returns to all of this. At some point, the Laffer Curve maximizes, and any further cuts cost the government money. Similarly, the trillionth stimulus dollar probably isn't nearly as effective as the first.