Bob responds to Brad DeLong and suggests Krugman's buttressing his point.
Errrmmm... only if you had a really bizarre perspective on this in the first place.
Perhaps Bob should take Krugman’s post as evidence that nobody disagreed with him on the relationship between investment and potential output (that this is not just something that Austrians and Larry Summers have come up with).
I feel like I have a decent grasp of the way Bob thinks, and I'm honestly baffled how he could write that in the first place. And maybe he doesn't think that, it's just a little rhetorical flare (that would make me feel a lot better). But if he does, maybe that's the place to start.
That would imply that the disagreement is elsewhere – over the degree of the effect and the strength of DeLong’s initial point. Bob seems to think that DeLong is using a particular meaning of “materially lower” and he is hanging an awful lot on the assumption that Brad is using that phrase in that way.