It's a fact, documented by two recent studies, that registered Republicans and self-proclaimed conservatives make up only a small minority of professors at elite universities. But what should we conclude from that?
Conservatives see it as compelling evidence of liberal bias in university hiring and promotion. And they say that new "academic freedom" laws will simply mitigate the effects of that bias, promoting a diversity of views. But a closer look both at the universities and at the motives of those who would police them suggests a quite different story.
Claims that liberal bias keeps conservatives off college faculties almost always focus on the humanities and social sciences, where judgments about what constitutes good scholarship can seem subjective to an outsider. But studies that find registered Republicans in the minority at elite universities show that Republicans are almost as rare in hard sciences like physics and in engineering departments as in softer fields. Why?
One answer is self-selection - the same sort of self-selection that leads Republicans to outnumber Democrats four to one in the military. The sort of person who prefers an academic career to the private sector is likely to be somewhat more liberal than average, even in engineering.
Krugman looks at other issues as well. Personally I've thought for some time that valuing facts over ideology brings one naturally to a liberal position. In other words, those who are members of the "reality based community" are liberal because liberalism is supported by the facts when they are honestly examined. Educated people tend to value the evidence over dogmatic assertions.