Zuh? Krugman's big success came from his work in international economics (the Clark Medal for stuff on currency crises and the Nobel for new trade theory, iirc) and I don't think any of it would be categorized as "Keynesian" per se. He spent the 90's arguing for lower trade barriers against protectionists like Robert Reich, so it's not like he got his spot at the NYT for being dogmatically progressive. Plus he's lavishly praised Milton Friedman's work as an economist, yadda yadda.
Krugman certainly doesn't treat a particular economic theory as "absolute" as much as, say, Ron Paul.
But the more important thing is what the good Admiral was getting at. Krugman keeps going on the record with explicit, falsifiable predictions: the Bush cuts would raise the deficit, the early 00's recovery would be driven by a housing bubble rather than business investment, housing prices were in line for a correction by the mid-late 00's, the Obama stimulus would leave unemployment at ~9%, US interest rates would remain low, the US was in danger of a liquidity trap where Fed policy wouldn't spur a recovery, struggling countries in the Euro zone would have particular problems because they can't devalue their currency, forced austerity wouldn't produce investor confidence in Greece, etc.
A lot of these are cases where he's been in the minority, and all of them were cases where there was serious disagreement. And all he does is get it right over and over. Seriously, who out there has a better track record in predicting what was likely to happen, or who did a better job explaining why? Even if you don't like his politics, at some point he's gotta become hard to ignore.
