U Chicago law prof Richard Epstein:
There is no question that if law professors were arrayed on a one-dimensional liberal to conservative line, the majority would be toward the liberal end. The interesting questions are two.
First, just what would the distribution look like? This is hard to gauge without some detailed work, but on average I would say that there are more left-wing democrats than center-left democrats. I define the difference as follows. The former are those who have sympathy for programs of redistribution on such key areas as education and health care, but are by and large supportive of market institutions on the production side of the line. There is an effort to make good on the earlier social democratic tradition. The left democrats are in favor of a larger public sector and are deeply suspicious of markets more or less across the board. To put the point most vividly, the center left group is uncomfortable that Obama is too far to the left. The left liberal group is uncomfortable that he is too far to the right. There is a lot of difference there.
On the conservative side there is also a break of a different order, between social conservatives and libertarians. There are some people who are both, but neither group is represented in large numbers. I have not done any empirical work, but my own sense is that a larger fraction of the right of center law professors are active in scholarship than on the left, which changes the public discourse.
Second, there is one factor that mutes these differences in many instances. Law is a profession, and you have to know such things as the civil rules of procedure and corporations. The subject matter requires technical knowledge. There are right and wrong answers. The gap therefore among law professors may be large on such questions as do we believe in constitutional originalism. But by the same token, the technical and professional anchor tends to bring the two sides closer together, for the great benefit of the profession. That is perhaps why it is often hard to figure out where academics stand on the political spectrum from reading their legal writings.