In his review of Greenspan's book, DeLong is positively gushing, saying that Greenspan's record as Fed chairman is "amazing", and "certainly much better than most economists I know could have done"; he even calls Greenspan a "veritable rock-star economist-technocrat".
It's all a bit weird: why would DeLong, a man of the left, spend so much effort defending the record of an Ayn Rand disciple who describes himself as a libertarian Republican and who is generally credited with smoothing the path to a series of fiscally disastrous tax cuts in 2001?
Maybe one hint can be found in Dan Okrent's review of Greenspan's book:
Surprisingly for a self-described "lifelong Republican," Greenspan was happiest as Fed chairman when Clinton was in the White House. (He also liked his time running Ford's Council of Economic Advisors, where it was his pleasant responsibility "to shoot down harebrained fiscal policy schemes.")
With the first George Bush, Greenspan had what he calls a "terrible relationship."
He faults the administration of Bush II for a -decision-making process driven entirely by political calculation.
By comparison, he found the Democratic interregnum sandwiched between two slices of Bush a version of Periclean Athens, where dedicated men (Bob Rubin, Larry Summers, Clinton, himself) made decisions in the nation's long-term interest.
DeLong himself was an important economist-technocrat within the Clinton administration, along with Rubin and Summers and Greenspan himself. He might not have achieved rock-star status (except within the blogosphere, and that came later), but I daresay that Greenspan would be happy to give DeLong some credit for his contributions to this Periclean utopia.
If Krugman had joined the Clinton administration while DeLong became more of an economics popularizer and columnist, might their views of Greenspan be different today? Probably not, but I'm not sure where else this big gap between the two might have come from.