Krugman discovers a January 7, 2009 Statement from then President-Elect Obama on the stimulus and reasons:
Aside from the fact that Obama was being cautious about the deficit when he really, really shouldn’t have been, think about how this has actually played out. A weak stimulus together with caution on other fronts, including mortgage relief, led to a weak economy in 2010. This led to a big GOP victory in the midterms. And this led to Republican success in getting the high-end Bush tax cuts extended for two years and quite possibly indefinitely — which will do far more damage to the US debt position that a bigger stimulus in 2009 would have done.
A President is at the height of his political power in the first year of his Presidency. Undershooting on the stimulus (I know the argument, this was all he could get, but the evidence belies that assertion imo - he could have asked for more to settle for less, as George W. Bush did with his tax cuts in 2001), coupled with Tim Geithner's incompetence on the homeowner crisis (HAMP'd!) truly put the Administration behind the 8 ball. This Original Sin explains why a Dem "victory" on the debt ceiling will be limiting the cuts in spending the GOP will extract.
It is claimed that a "new" Obama has learned to play the game. I hope so, but the field has now overwhelmingly tilted against good economic policy. We seem doomed to relearn the lessons of 1938.