“The report of my death was an exaggeration,” Mark Twain told the New York Journal in 1897. The author had clearly contemplated the state of the conservative college professor in 21st century America, for whom warnings of extinction could be understating the case.

The ranks of right-leaning academics are dwindling, as college campuses trend toward ideological homogeneity and some professors are choosing to leave as they lament the failed promises of liberal education in America.

“Harvard students are not being well served,” a professor of government at Harvard, Stephen Rosen, who retired this year and will now mentor conservative military veterans for political careers, told the Sun. “You’re supposed to go to a liberal arts university to get shaken up, not to have your views confirmed.” 

A philosophy professor at Portland State University, Peter Boghossian, resigned last year for the same reason. He wrote to the school’s provost that “brick by brick,” the university has made true “intellectual exploration impossible.”

The academic Jordan Peterson resigned in January from his tenured professorship at the University of Toronto because his graduate students, sharing his “unacceptable philosophical positions,” faced minimal chances of attaining university research positions. 

Mr. Peterson asked, “How can I accept prospective researchers and train them in good conscience knowing their employment prospects to be minimal?”

A tenure-track professor since 1996 at the University of California, Los Angeles, Joseph Manson, is also retiring “because the Woke takeover of higher education has ruined academic life,” he said on his website. Mr. Manson decided, simply, “I’m getting out.”

Professors Val Rust, James Enstrom, Keith Fink, and Gordon Klein were also ousted from UCLA for dissenting from progressive university policies. Jonathan Katz was pushed out of Princeton by “the cancel culture mob.” Dorian Abbot had his prestigious lecture at MIT canceled following outrage on Twitter for his defense of academic evaluations based on merit. 

Mr. Abbott portrayed himself as a victim of a “woke ideology” that “is essentially totalitarian in nature: it attempts to corral the entirety of human existence into one narrow ideological viewpoint and to silence anyone who disagrees.” 

More than 80 percent of Harvard College faculty characterize their political leanings as “liberal” or “very liberal,” according to a survey by the Harvard Crimson. The school has not appointed a conservative faculty member in the past decade. 

At 90 years old, a professor of government, Harvey Mansfield, is widely viewed as the last such conservative professor. “They let me speak. It’s just that they never listen to me when I do speak,” Mr. Mansfield told the Sun, with a laugh.

He has repeatedly urged the university to hire more conservative faculty, explaining that “liberal and conservative professors say very different things.” Even supposedly nonpartisan scientists can unintentionally advocate for progressive positions in the classroom and fail to give equal consideration to alternative points of view, Mr. Mansfield said.

With a high number of tenured professors and few openings for new ones, the stakes at universities nationwide are high. “Most people, when appointments are being made, have strong beliefs that people who are like themselves are the ones who should get the appointment,” Mr. Mansfield said.

Nearly a quarter of American academics favor ousting a colleague for having a so-called wrong opinion about hot-button topics like immigration, according to a recent study from a libertarian think tank, the CATO Institute. 

Another study, by the Challey Institute for Global Innovation, notes that nearly 70 percent of students believe they should report a professor who says something they deem offensive.

“Everybody used to say: Be skeptical, prove it to me,” Mr. Rosen said. “Now, it’s: I’ll speak to you if you’re on the side of the angels; however, I define what the angels are.” 

Mr. Mansfield recalled what an Iranian student once told him: “In Iran, you have to be very careful about what you say in public, but what you say in private, that’s pretty free. At Harvard, it’s the reverse: You have to be very careful in private.”

“Human nature is on our side,” Mr. Rosen insisted: When everyone is touting the same ideas, someone has to question them. “Totalitarian societies are always undermined from within.”