http://krugman.blogs.nytimes.com/2010/12/07/the-deal/"Well, for starters we have the two-year extension of the Bush tax cuts. As I pointed out yesterday, the CBO estimated that such an extension would reduce unemployment relative to what it would have been otherwise by 0.1 to 0.3 percentage points in 2011, twice that in 2012.
To this, the deal added $120 billion in a payroll tax cut; $56 billion in extended unemployment benefits; about $40 billion in extension of other tax credit. Also, expensing of business investment.
I’d discount the last item: we’re awash in excess capacity, and likely to stay that way for years, so I don’t expect business investment to be noticeably affected by tax breaks that give an incentive to move spending up in time. The rest is about $220 billion, or about 0.75 percent of GDP over the two-year period. What’s the multiplier on that? Pretty high on UI, which will get spent; less on the rest. Overall, probably less than 1. So let’s say that this raises GDP by 0.7 percent relative to otherwise; rule of thumb is that one point on GDP is half a point on unemployment, so add 0.35 points to the CBO numbers."
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Krugman's argument is the political consequences of taking the deal are not worth preventing the economic damage from "no deal." That is a political conclusion. He is NOT saying that "no deal" would not significantly hurt the economy.