Krugman is more like Chomsky -- he did some academic work (including a good textbook in microecon), but then left that to do politics, almost entirely disconnected from his academic record.

The Econ "Nobel" is a little more rationally awarded than the Nobel Peace Prize, but neither is the same as Physics/Chem/Medicine.

I think it's fine to judge Krugman's political arguments on political merits; there isn't "nobel-caliber" economics behind them. They're usually about things which economics doesn't even address.