Mr. Mansfield’s study of manliness is acutely topical today, what with the #MeToo movement and the cries of “toxic masculinity” on college campuses, coupled with a startling masculine eruption in the White House. One wonders if there is a connection between the near-banishment of manhood from America’s social sphere and its sudden prominence in the political one. Although, it must be said, there are strong men in powerful positions elsewhere, too, including Russia’s Vladimir Putin, China’s Xi Jinping, Turkey’s Recep Tayyip Erdogan and India’s Narendra Modi.

“Let’s look at the Washington, D.C., kind of manliness,” Mr. Mansfield says. “Trump’s manliness is of a raw character, the kind you find, also, in Erdogan and Putin, who are rough and gross and discourteous.” In the Mansfield scheme, there’s a hierarchy of manliness, ranging from animalistic strength on the bottom rung, then rising gradually to gentlemanliness, and then to “the highest form, philosophic manliness: the willingness to take on dominant opinions and subvert them by questioning and argument.”

The “raw type of manliness,” Mr. Mansfield says, “coincides with a political situation of polarization.” A polarized democracy is “an invitation to the vulgar. I think what’s interesting about Trump is not so much Trump himself as the people who voted for him.” They are a reminder that democracy “wants equality, but the equality it gets tends to be at a lower level than the best.” America could, he suggests, have equality like the ancient Spartans, “requiring everyone to be courageous. But that’s too difficult for us and doesn’t answer our needs.”

We are in Mr. Mansfield’s home, a garrison colonial hidden behind a high fence, and at this point in the conversation a bustling German lady enters from the garden, her face flushed from the cold. She is Anna Schmidt, Mr. Mansfield’s third wife. (His first marriage ended in divorce, and his second wife, with whom he collaborated on a masterful translation of Tocqueville’s “Democracy in America,” died of cancer in 2006.) She gives the impression of being twice as tall as the modestly built professor, and at 43, she’s half his age. With a certain amount of hamming it up about her duties in the kitchen, she disappears to cook dinner.

Mr. Mansfield, who betrays a visible pride in Mrs. Mansfield, returns to the subject of Mr. Trump’s supporters. “They rather like and appreciate his vulgarity and his baseness, his impulsiveness,” he says. “It doesn’t bother them that he’s rich and wears flashy, bright ties.” They think “that this is how they would be if they were rich. Trump is an image of their notion of what money can buy.”

In 2016, Mr. Mansfield continues, Mr. Trump won “a majority of white women—and women are attracted to manly men, I think.” He agrees that there’s a connection between the campaign for gender-neutrality in the U.S.—seeking, as he sees it, to erase all differences between the sexes—and the “hunger” that made Mr. Trump’s political rise possible.

In Mr. Mansfield’s view, Mr. Trump’s success wasn’t a racial reaction to President Obama as much as a backlash in favor of masculinity. Mr. Obama “had the scolding demeanor of a schoolmarm—very much, I think, following the temper of today’s feminists. It’s all a matter of correcting the behavior of misbehaving juveniles, and of condescension.” Here, he checks himself, allowing that this observation “is a little unfair to Obama, because some of his speeches were pretty good, and he did have a vision of America and the way America ought to be.” But it was not an America that “throws its weight around. That’s precisely what he wanted to avoid. So, in his foreign policy, and in his domestic role as condescender-in-chief, he showed his hostility to manliness.”

Mr. Trump saw the electoral opportunity. “Trump’s not a clever man,” Mr. Mansfield says, by which he means that the president has little propensity for abstraction or intellectual complication. “But he’s shrewd. He saw that there was a way to be appealing, and to knock off the competition of his rivals in the Republican Party, by a display of manliness and an attack on political correctness.” Mr. Trump is “really the first American politician to use that, to see that there was a political opening there.”

Laughing lightly, Mr. Mansfield recalls Mr. Trump’s masculine belittling of “Little Marco,” “Low Energy Jeb” and “Lyin’ Ted.” “That was very effective with a lot of voters,” he says, “particularly the less educated. You could look at 2016 as a revolt of the lower-IQ half of America against the upper half, which is dominated by the universities.” Now in Washington there has been “a replacement of the people who reflect the values of American universities, where manliness is taboo.”

The Trump election, Mr. Mansfield muses, is one sign that the steady march of gender-neutrality is slowing and may even be halted. “We haven’t had a real political debate about manliness,” he says, “and maybe Trump is the first stage of it.” Mr. Trump presents issues “in a manly way, which is to say, ‘Take it or leave it.’ Like the wall—the wall is an intransigent object that justifies and encourages an intransigent mode of speech.”

Similarly with “Make America Great Again,” Mr. Trump’s political shibboleth. “It invokes the manly, and allies it with patriotism,” Mr. Mansfield says. “And the ‘again’ is a strong critique of recent presidents, because it states that ‘we had it once and we lost it, thanks to you.’ ” Mr. Trump could have said “Make America Manly Again,” Mr. Mansfield says. “That would have been too much. But I believe that’s what he meant.”

The thrill of competition is an intrinsic part of Mr. Mansfield’s idea of manliness, which suggests that, in his worldview, political campaigning is an inherently masculine pursuit. “American elections,” he agrees, “have traditionally been, in great part, tests of manliness.” Was the last election a test of Hillary Clinton’s manliness as well? “Yes it was,” Mr. Mansfield responds, “and she showed it a certain amount. Maybe it’s difficult for a woman to do that in a graceful way, and to maintain her femininity.”

Mr. Mansfield isn’t sure whether Mrs. Clinton lost in 2016 “because of electoral difficulties in being a woman, or just because of the kind of woman she was. It would be necessary to untangle those different possibilities.” He adds that Margaret Thatcher, who won three terms as Britain’s prime minister, “is one of my models of manliness.”

If Mr. Trump’s manliness is vulgar, which presidents’ were refined? He’s quick to cite the Bushes—“almost courtly, but friendly; people who couldn’t be pushed around and who had a controlled anger.” One of the chief attributes of a good politician, Mr. Mansfield says, is knowing “how to be angry in an effectual and impressive way, without losing it.”

Mr. Mansfield doesn’t see it as an accident that Mr. Trump’s presidency coincides with an impressively indignant national movement against sexual harassment. #MeToo, he believes, “is really directed at Trump, and people like him, accusing them of being ‘deplorable.’ ” (He uses that “Hillary word,” as he calls it, deliberately.) The movement “represents a particular critique of Trump for his sexual harassment, or at least his lamentable sexual reputation. It’s against the aggressive male, the presumptuous male, the male who hasn’t had his ‘consciousness raised’ sufficiently. That’s Trump, and the #MeToo campaign sees him as the embodiment of everything male they don’t like, and want to oppose.”

Yet Mr. Mansfield sees a “contradiction” in Mr. Trump’s manliness: “It’s his ‘art of the deal.’ A person who makes a deal all the time is unmanly, just as economics is inherently unmanly because it always wants a trade-off.” A manly person “stands for things, and when you stand for something, that means you’re not willing to make a deal against it.” He views Mr. Trump’s recently announced tariffs as a way “to get him to a deal.”

He doesn’t expect Mr. Trump to change over the course of his presidency—to acquire more polish or refinement. “He’s had a chance to do that,” Mr. Mansfield says. “He’s an unapt pupil, a rebellious pupil. But his alliance with the Republicans seems to be based on the realization that—and here I give him some credit—to make America great again he has to be a success as president.”

Mr. Mansfield is, however, critical of Mr. Trump’s dealings with Kim Jong Un. “It’s a personal contest between him and this tin-pot dictator,” he says. “The crisis needs some delicacy to obtain what needs to be a siege, and a blockade. That requires allies and aggressive, pushy diplomacy.” Mr. Trump “doesn’t have the patience, and he has that in common with the American people. This is in Tocqueville, so it must be right—that democracy is ‘impatient.’ ”

Still, Mr. Trump’s manliness is playing out differently in the rest of the world from its reception in America—and North Korea. “He doesn’t seem to have the fans abroad that he does here,” Mr. Mansfield says. “But in order for him to be successful outside America, he doesn’t have to have fans. He just has to have people impressed and a little perturbed.”

Mr. Trump has the world’s attention, for sure, and “it’s possible that he could use it for some positive purpose.” Europe, Mr. Mansfield says, “was just falling asleep by stages. Now, Trump is worrying them. . . . That’s good, isn’t it?”

Mr. Varadarajan is a fellow at Stanford University’s Hoover Institution.