Is "You're a racist" an opinion, or a statement of fact?

Yesterday, I posted a story about a law professor who has sued several former students after they made what he characterizes as false accusations of racism.  I don't know the professor involved, or anyone at the school.  But it seems like this case is a dog.

Some of the comments to the original Above the Law story have already pointed out the interesting position the plaintiff will find himself in as a result of the constitutional elements of a defamation claim.  Plaintiff will likely have to argue that he is not a public figure; the defendants can introduce promotional materials shipped out by the Dean at the school touting the plaintiff's national influence and prominence.

The more fatal problem seems to me that accusing someone of being a racist isn't a statement of fact, it's an opinion and therefore privileged.   The heart of the defamation claim surrounds the accusation that this professor is a racist or behaved in a racist manner.  But is this objectively verifiable?   Is it "susceptible of being proved true or false susceptible of being proved true or false"? Milkovich v. Lorain Journal Co., 497 U.S. 1 (1990).  Suppose I announce that my neighbor, who is moving to the suburbs from our diverse urban neighborhood, is moving because he is a racist.  How can we verify one way or another what the motives for his move might be?

Surprisingly, there is case law out there in which the accusation of racism was held to be actionable in defamation, but these cases may be a bit outdated:

Appellant contends that as a matter of law the article is not libelous, since Mr. Stone did not flatly state that plaintiff was prejudiced, and because it is not a statement of fact about plaintiff's conduct but a statement of opinion about his attitude. Where readers would understand a defamatory meaning liability cannot be avoided merely because the publication is cast in the form of an opinion, belief, insinuation or even question.  A statement about one's attitude is defamatory if it tends to lower him in the esteem of the community. See Christopher v. American News Co., 171 F.2d 275 (7th Cir. 1948), where it was held actionable to charge that one is pro-Nazi.

Afro-American Pub. Co. v. Jaffe, 366 F.2d 649 (D.C. Cir., 1966)

I haven't seen the professor's complaint, so I don't know what the students said that he specifically questions, other than what's been reported in the press.  While there may have been specific assertions of fact in the students' letters and communications regarding this professor ("He said . . . ", "He did ..."), had the students simply made a characterization of the professor as a racist, without asserting particular conduct, they would likely be safe from suit. 

That the faculty and dean would ever let relations with minority students get to this point seems to reflect a fatal lack of communication at the law school.