The Keynesians can't possibly come up with answers to those questions that make any sense in the real world.
As Albert Einstein said, insanity is doing the same thing over and over again and expecting to get different results, and the Keynesians utterly qualify as insane.
I think that is what Krugman’s entire theory is based on. Why not spend infinite sums if you are going to get a $1.60 muliplier?