It gives some of those excess savings a place to go -- and in the process expands overall demand, and hence GDP. It does NOT crowd out private spending, at least not until the excess supply of savings has been sopped up, which is the same thing as saying not until the economy has escaped from the liquidity trap. His own addition to that quote was to say that: .. both the US and UK have had deficits running at historically extremely high levels, and long-term interest rates at historic lows: as Krugman has repeatedly pointed out, the (IS-LM) textbook has been spot on ... So score one for macro 101. So in their minds, the only reason that the increased budget deficits have not driven up interest rates is because the world is stuck in a liquidity trap. There are several different strands of mainstream economic thinking and these differences manifest in the way they think about monetary and fiscal policy. The extreme mainstream position is that fiscal policy is ineffective because it 100 per cent crowds out private spending. The only role for aggregate policy then is to allow an independent (politically speaking) central bank to adjust interest rates up and down to regulate inflation (via expectations). There isn't much for economists to do if that view was accurate. Then there are mainstreamers who think that budget deficits are generally damaging to private spending because they drive up interest rates and crowd out private spending, the latter which,