Krugman opposes the deal because he does not think that the deal will put the economy on the right trend in 2012. Most of the stimulus will occur in 2011 and the economy will flatten out again before the election. The GOP will extend the Bush tax cuts which will worsen our deficits and facilitate the use of the GOP "starve the beast strategy".
The comments that follow are quite interesting reading. I was reminded of what Obama told some of his fellow democrats during the healthcare debate. He said that doing the right thing for the country's longer term future was more important than winning the next election. It seems to me like he is not taking his own advise when it applies to himself.