The left-wing threat to campus free speech is abating. The right-wing threat is not.

When it comes to free speech on American campuses, there seems to be a law of conservation at work: Just when the internal threat of censorship from left-wing campus activists is abating, the external threat from right-wing lawmakers is rising. But given that the new threat relies not on the decibel level of immature 18-somethings but the state power of motivated adults, it may be much harder to fight.

Concerns about political correctness on campus date back at least 25 years when Philip Roth wrote The Human Stain, his brilliant...