I've never thought much of Paul Krugman, the NY Times' designated liberal economist, although he recently saw the light, sort of, on the wage impact of immigration.

But he has just indulged in an unpardonable stereotypical slur:

[K]now-nothingism - the insistence that there are simple, brute-force, instant-gratification answers to every problem, and that there's something effeminate and weak about anyone who suggests otherwise - has become the core of Republican policy and political strategy. The party's de facto slogan has become: "Real men don't think things through."[Know-Nothing Politics, New York Times, August 7, 2008]

Krugman was making the boring claim that the Republican energy policy is simplistic. But he's slurring the "Know-Nothings", the much maligned 1840s-1850s patriotic immigration reform movement. They were called "Know-Nothings", not because they literally knew nothing, but because they were instructed to say they knew nothing if they were questioned about their Masonic-style oath. In fact, as I reported thirteen years ago (!) in Alien Nation,

...the Know Nothings were far from an ignorant mob, as immigration enthusiasts, probably misunderstanding that nickname, tend to assume. Recent research has shown that they were a cross section of solid middle- and upper-middle-class citizens.

A source for this: Tyler Anbinder's Nativism And Slavery (1992).

Krugman probably meant "Neanderthal". But no doubt he couldn't resist a chance to smear patriotic immigration reformers—and he certainly wouldn't want to be accused of species-ism!