On Monday, "Breaking Bad" actor Bryan Cranston called Donald Trump a “supreme narcissist.”

On Tuesday, Washington Post columnist Dana Milbank referred to Trump’s convention appearances as "the triumph of narcissism."

And by Wednesday, Tony Schwartz, ghostwriter of Trump’s bestselling book, “The Art of the Deal,” had made sure he’d told everyone from Jane Mayer at the New Yorker to TV’s Bill Maher that Trump’s narcissistic self-absorption had made him a “sociopath.”

For the four days of the Republican convention, the word “narcissism” was never more in vogue, but what does the word actually mean? More importantly, what would it mean for America if one of the nominees for president of the United States is a narcissist? Aren’t all politicians?

“Narcissism is a trait all human beings have to one extent or another, so it’s not inherently negative,” said psychologist Margaret Jordan, an expert in personality disorders at Houston’s Baylor College of Medicine. “It’s a part of self-esteem and is important to mental health.”

So when does self-regard become pathological?

Experts say all people have some narcissistic traits, but what does being a "narcissist" mean? (Victoria Walker/The Washington Post)

The most recent edition of the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders describes narcissistic personality disorder as being “characterized by the presence of both grandiosity and attention seeking” and lists nine criteria, of which five are necessary for diagnosis. Among them: a need for excessive admiration; preoccupation with fantasies of brilliance, power and success; and a sense of being special.

Those traits can lead to arrogance and haughtiness, and a single-minded pursuit of status that make close relationships difficult and devoid of true intimacy.

A half-dozen clinicians contacted for this story said that it would be unethical to diagnose Trump, someone they had never treated, with having pathological narcissism or any other mental condition. This constraint, commonly referred to as the Goldwater Rule, arose after an incident in the 1964 presidential race between Barry Goldwater and Lyndon Johnson. Prior to the election, more than 1,100 psychiatrists were polled about their views of Goldwater’s mental status. Most of their responses were not positive. The American Psychiatric Association later warned its members against diagnosing public figures.

But a number of clinicians agreed to discuss how they would evaluate possible signs of narcissistic personality disorder. Asked to give an example, more than one expert cited the tweet Trump sent out just hours after the Orlando nightclub massacre last month: “Appreciate the congrats for being right on radical Islamic terrorism.”

Trump has said that his “IQ is one of the highest,” that he has “the world’s greatest memory,” and that he is “dazzled” by his own creations.

And during his speech Thursday night at the Republican convention, he faulted the government’s “broken system,” then declared: “I alone can fix it.”

Donald Trump spoke for more than one hour, we broke it down to less than five minutes. (Deirdra O'Regan/The Washington Post)

Jonathan Moreno, a bioethicist and science historian at the University of Pennsylvania, felt freer as a non-clinician to speculate on Trump and narcissistic personality disorder.

“He sure seems to meet the criteria,” Moreno said. “The question is, is it pathological. That’s a judgment I can’t make.”

(His father, Jacob Moreno, a psychosociologist and the founder of psychodrama, was one of the doctors surveyed about Goldwater in 1964. “He was very upset with himself for answering,” Jonathan Moreno recalled.)

Psychiatrists say narcissism appears to run in families. What is known about Trump’s father, Fred, is that he was authoritarian, ruthlessly ambitious and encouraged his second son, Donald, to be both a “killer” and a “king.”

Trump has occasionally expressed qualified admiration for vainglorious, even despotic rulers of the past. At a rally in North Carolina, he said former Iraqi leader Saddam Hussein was “a really bad guy. But you know what he did well? He killed terrorists.”

On more than one occasion, Trump has compared Obama’s leadership, unfavorably, to North Korean tyrant Kim Jong Un and Russian President Vladi­mir Putin.

Watch: Donald Trump and Vladimir Putin: A bromance (Gillian Brockell/The Washington Post)

A simple narcissist is someone who is self-absorbed, says Peter Freed, a psychiatrist at the Personality Studies Institute in New York City. On the other hand, people with narcissistic personality disorder are so self-absorbed that they are indifferent, even oblivious, to how they appear to others. If, however, those with narcissistic personality disorder feel they have been overlooked, disregarded — or worse, insulted — they quickly become “ashamed of their inadequacies,” Freed added. The response is unconscious, but so powerful that “they wear a grandiose shell around them that deflects the shame.”

Trump’s first wife, Ivana, once told a reporter that when she was dating the real estate mogul, she whizzed past him at one point on a ski slope. Irate, he responded by taking off his skis and walking the rest of the way down the hill.

In the late 1980s, way before Marco Rubio ever referred to the diminutive size of Trump’s hands (thereby questioning his masculinity), Graydon Carter was the first to cast aspersions on Trump’s digits. At the time, Carter, now editor of Vanity Fair, was the co-founder of the satirical magazine Spy. In its pages he repeatedly referred to Trump as a “short-fingered Vulgarian.” More than a quarter-century later, Carter would still occasionally receive an envelope in the mail from Trump, usually with a news photograph of The Donald, his hands circled in gold Sharpie to highlight what he says are normal-sized fingers.

In his book "The Art of the Deal," Trump wrote: “When people wrong you, go after those people, because it is a good feeling and because other people will see you doing it. I love getting even.”

Pathological narcissism is not, strictly speaking, a mental illness. Rather, it is classified as a personality disorder, afflicting someone whose behavior and beliefs lie far outside the norm. Unlike many mental illnesses, the origins of personality disorders are generally considered more familial and environmental than genetic.

Freed thinks narcissism is the “great, undiagnosed character pa­thol­ogy of the modern age,” even though few in psychiatry want to even use the word narcissism, he says, because of its pejorative connotation. The American public “is hampered by a lack of education about a syndrome that is real” and causes “real suffering.”

Ultimately, he said, regarding highly successful people, narcissism works — until it doesn’t. Usually those who suffer most are not the narcissists, Freed says, but those around them, the people who have to cope with the “mood swings, walking on egg shells, the demand to be sycophantic.”

“Right now Trump is not having a hard time” he said. “The hard time will come if he loses.”

A study published in the journal Psychological Science measured how 42 presidents rank on a “grandiose narcissism" scale. Can you identify the top five?