Tunku Varadarajan gathers important insights about higher education’s current state from a Harvard expert.

If you want the long view of what’s gone wrong with American higher education, you could do worse than talk with Harvey Mansfield. Mr. Mansfield is 92, and he taught at Harvard for well over half a century, retiring from the government department only last year. A scholar of Machiavelli and Tocqueville, he is a lifelong conservative. He says he leaves behind a department with only one professor “who isn’t a liberal or progressive.” That “self-professed conservative” is Eric Nelson, 46, who studies the political thought of the early modern Western world.

The department had much more ideological diversity when Mr. Mansfield arrived at Harvard as an undergraduate in 1949. Then, “1 out of 3 professors would have been Republican,” he says. His mentor was Samuel Beer (1911-2009), “my big teacher all the way through from undergraduate to Ph.D.” Beer was an expert in British government, “as no one is anymore.”

Beer was also a Democrat. …

… By 1969, when Mr. Mansfield was appointed as a full professor, political liberals were beginning to pack the department with their own kind. But “those were still liberals,” he says, “who were willing to appoint somebody like me, who was an opponent of what they believed.”

The American academy has turned hyperpartisan since those days. The left-liberal Boston Globe asked in a February headline: “Will Harvard ever get another professor like Harvey Mansfield?” The answer is almost certainly no. If Mr. Mansfield’s now-vacant university chair stays with the government department instead of being allocated to another faculty, it would be a near-miracle if Harvard were to appoint a conservative like him to the job he once held. Even liberals are outnumbered in the professoriate by those who style themselves progressives—no-holds-barred leftists for whom any ideological cohabitation is anathema.

How does Mr. Mansfield define the difference between a progressive and a liberal? A progressive has a “loathing for his country. It goes beyond embarrassment to real dislike of America, and in a way, therefore, of themselves, because after all they’re Americans.” Theirs is a kind of “fanatical penitentialism.”