This contrast of manly types could be seen as akin to the Freudian battle between self-assertion and social control. A shaven man was perceived as a team player, disciplined and sociable. A man with facial hair, by contrast, was more impulsive and independent, playing by his own rules.

It was for this reason that voters, from the 1920s onward, regarded mustachioed politicians with suspicion. If two-time presidential runner-up Thomas Dewey, whom one admirer dubbed the “Clark Gable of candidates,” had shaved his upper lip, history might have been kinder to him. In 1944, journalist Edith Efron wrote about Dewey’s mustache in The New York Times Magazine: “It fascinates. It amuses. And it repels.” His lip adornment helped Dewey achieve a reputation for toughness, but also for arrogance. After his 1948 defeat, Dewey only half-jokingly told some visiting boy scouts, “remember, fellows, any boy can become president unless he’s got a mustache.”

In subsequent years, facial hair was a feature of the rebellious left. In our times, it is still nonconformist in business and politics, though today one is just as likely to find it on the political right, which has increasingly developed its own rebellious counterculture. For every Che Guevara, there is a Geraldo Rivera; for every hairy hipster, a hirsute hunter. This brings us back to Mr. Bolton, and to Mr. Trump himself.

Mr. Bolton’s disregard for shaving norms is a faithful reflection of his fierce independence, and his general disdain for established political ground rules and diplomatic norms. His vitriolic language and passion for conflict prevented him from winning Senate confirmation in 2005 as ambassador to the United Nations. He is the ego in conflict with the super-ego of the political establishment: Negotiations and treaties are for wimps, and so are razors.

Reporters have noted that early in his presidency, Mr. Trump felt tentative, and inclined to listen to the advice of people around him. Today he is increasingly going with his gut, and worries far less about convention or conventional looks. As he throws off the shackles on his own ego, he has turned to a similarly liberated national security adviser. Even if he still does not like Mr. Bolton’s mustache, Mr. Trump may be drawn to the pugnacious manliness it represents.

In historical context, Mr. Bolton’s mustache fits perfectly for a man who follows no rules. No wonder he has vowed never to shave it off. And no wonder that, in spite of initial misgivings, the “Disruptor-in-Chief” has turned to him. Perhaps Mr. Trump will consider growing one himself some day.