This mild or subclinical state — “not in and of itself, an illness. It is a temperament” — characterizes many of the most successful American men, Gartner contends. He lists their distinctive traits:

He is flooded with ideas. He is driven, restless, and unable to keep still. He channels his energy into the achievement of wildly grand ambitions. He often works on little sleep. He feels brilliant, special, chosen, perhaps even destined to change the world. He can be euphoric. He becomes easily irritated by minor obstacles. He is a risk taker. He overspends in both his business and personal life. He acts out sexually. He sometimes acts impulsively, with poor judgment, in ways that can have painful consequences.

Gartner warns that this constellation of traits, which compel loyalty and support, can also lead “to impulsive behavior (ready, shoot, aim) and confident leaders who glibly take their followers over a cliff.”

Trump makes white working-class voters, the core of his support, “feel safe,” Gartner told me in a phone interview.

Poll data from the Pew Research Center shows how much Trump depends on the politically restive white working class. His backing from voters with a high school degree or less is twice as high as is it is from those with college degrees; the percentage of men lining up behind him is eight points higher than the percentage of women; voters from households making $40,000 or less are 12 points more likely to cast a Trump ballot than those from households making more than $75,000.

Unlike most Republican candidates, Trump rejects cuts in Social Security and Medicare — programs strongly supported by the white working class. And, while he nods in the direction of the anti-abortion movement, he does not attempt to impose a repressive sexual morality (after all, he has been married three times).

Gartner warns that the qualities that “get you elected are not the same as the capacity for governing.” Hypomanic individuals do not necessarily make effective presidents, he said, unless their “energy, optimism, and drive” are balanced by capacities that he thinks Trump might lack:

the capacity to study and evaluate, to cooperate, thoroughness, caution, attention to detail, the ability to make a firm decision based on reasoning.

Joseph Burgo, a psychotherapist and the author of “The Narcissist You Know,” put the logic of Trump’s appeal in straightforward terms:

For many people, Trump’s braggadocio, contempt, and grandiosity come across as self-confident strength. When frightened by dangers from abroad or here at home, many people gravitate to the ‘strong man’ who promises to vanquish their fears and confusion.

Lise Van Susteren, a forensic psychiatrist based in Washington, D.C., argued in a phone interview that Trump filled different roles for women and men:

Women right now feel an immense sense of insecurity, threatened by pervasive, random violence from shooters in Colorado to ISIS chopping off heads of innocent victims. To women, Trump represents security.

For less well-educated white men, Van Susteren said,

the last eight years have been humiliating. They have been emasculated by economic factors, unable to earn what they need — the jobs they want they perceive going to immigrants.” At the same time, these voters believe that “we are getting our butts kicked in the Middle East. For the white male, Trump offers a chance to have his sense of manhood restored. He conveys enormous confidence. Voting for Trump feels empowering in the sense that you can say what you believe without getting in trouble for it.

Stanley Renshon, a political scientist at CUNY and a psychoanalyst, also claimed in a phone interview that many in the electorate felt besieged. For these voters, Trump is “saying things what everybody thinks,” and in the process, he is

opening a public debate on subjects nobody wants to talk about, things that people feel misled or lied to about. Trump gives voice to the feeling of dismissal and mines the anger. And what is that anger, it’s the anger of ordinary Americans who feel they have been lied to, that the policies they have been promised don’t work, and, by and large, they feel they have not been taken into account. Trump says to them, “you are right. Watch me, I am making them take me into account. I’ll do the same for you.”

W. Keith Campbell, professor of psychology at the University of Georgia, noted in a phone interview that

Trust is at the lowest it’s ever been. There is a push for strong leadership, and Trump comes across as a strong leader.

Campbell, who distinguished himself from “liberal academics,” said “when I talk to normal people” the idea of “opening up to additional immigration when so many people are struggling to find good work just seems politically insane. Why should we bring in 200,000 Syrians?”

Trump is a high-risk candidate who is in constant danger of self-immolation. But not only has he outlasted a long list of controversies, he has thrived in their wake. As Campbell put it,

The fact that he is willing to do stuff that is completely against what a politician should be doing makes him seem all the stronger. He does not apologize.

Trump’s opponents fail to recognize that his apparent vulnerabilities — his hubris, his narcissism, his bullying, his boisterousness — have been strengths in a primary campaign premised on defiance of political correctness, left and right.

Regardless of the outcome, the somewhat brutish tenor of the Trump campaign will leave a significant legacy, a legacy implicit in the question posed by Karen Tumulty of The Washington Post, “Will Trump eventually cross a line — or do the lines no longer exist?”