Robert Murphy takes apart the Keynesian argument for more stimulus. He concludes with the following:

Brad DeLong’s recent arithmetical argument for bigger government deficits is flawed on several counts. He treats government spending as equivalent to household spending, and his focus on aggregates overlooks the coordinating function of interest rates. In the end, he offers little explanation of how letting politicians borrow an extra $100 billion to spend on anything at all could possibly make the whole country richer.

To follow his argument, read his full piece, DeLong on Deficits.