Republicans facing a near-daily grilling about Donald Trump’s views on Muslims, a giant border wall with Mexico or a possible trade war with China should probably start prepping for a more fundamental question: “What’s wrong with this guy?”

Trump’s erratic behavior has been carefully followed by the political class and some Republican primary voters. But millions of general election voters -- and even some GOP donors -- are just tuning in to Trump's high self-regard and proclivity for misstatements.

“Okay, so our guy is insane,” said one GOP fundraising bundler privately after getting his first up-close view of his party’s presidential nominee at a recent California fundraiser.

Trump so loved the adulation of attendees that he insisted on taking photos with everyone there, rather than just those who’d donated the threshold amount. Trump blew his schedule for the day as a result.

Trump’s campaign did not respond to The Huffington Post's queries on the topic.

As it happens, some mental health professionals have been pondering Trump’s state of mind for months, and appear to have arrived at a consensus. From his exaggerated claims of immense wealth and his aggressive insults against those who challenge him, to his expectation that all Republicans should fall in line to support him, Trump exhibits symptoms of what the American Psychiatric Association defines as narcissistic personality disorder.

“The boldness, the risk-taking, the attention-seeking, are classic narcissistic traits,” said W. Keith Campbell, a University of Georgia psychology professor and co-author of The Narcissism Epidemic: Living in the Age of Entitlement.

The only real question: whether Trump merely possesses many of the traits, or if his condition warrants the full-on label of “disorder."

“I don’t like throwing out the term" narcissistic personality disorder, Campbell said. “That’s a clinical diagnosis.”

None of the experts contacted by The Huffington Post was willing to offer a diagnosis for Trump. That may be because it's difficult to diagnose anyone without a personal examination -- or it may be a result of the 1964 presidential election, when a number of psychiatrists responding to a magazine survey said Republican Barry Goldwater was unfit to be president. Goldwater lost the election in a landslide, but won his libel suit against the magazine.

In any case, said Columbia University psychiatry professor Robert Klitzman, the severity of the condition is a matter of degree, with the disorder diagnosis reserved for those whose symptoms are so severe that they affect the person’s ability to function.

“He managed to mount a national campaign to get millions of people to vote for him,” Klitzman said of Trump. “It's hard to say that someone in that position has a disorder."

Whatever the severity of his condition, many of Trump's actions and statements through the years that may have appeared bizarre on their face make more sense in the context of the symptoms:

Claiming wealth exceeding $10 billion, when every independent estimate has been at most half of that? “Exaggerating your achievements and talents,” is trait No. 3 among the dozen listed on the Mayo Clinic’s description of the disorder .

Mayo Clinic’s description of the disorder Believing the Republican National Committee and its donors should handle all the fundraising and voter turnout details for his general election campaign? Here’s trait No. 8: “Expecting special favors and unquestioning compliance with your expectations.”

Pretending to be a publicist to plant the false story that he was dating Italian supermodel Carla Bruni? Trait No. 4: “Being preoccupied with fantasies about success, power, brilliance, beauty or the perfect mate.”

Even Trump’s months-long feud with Fox News host Megyn Kelly over her tough questioning at a GOP debate last summer may fit the disorder’s characteristics. A Kent State University study published in 2010 showed that narcissistic men were far more prone to harbor hostile attitudes toward women -- because women held the power to harm their self-esteem.

Some narcissistic traits, the researchers pointed out, are not necessarily a bad thing in presidential candidates.

“They can be helpful in getting people to believe in you, in getting out there and working hard, in getting your agenda through,” Columbia’s Klitzman said, adding that past presidents like Theodore Roosevelt, Franklin Delano Roosevelt and Lyndon Johnson all exhibited narcissistic traits, but managed to function effectively in office.

“Anyone running for president either has a high level of narcissism or is being funded by someone with a high level of narcissism,” said Campbell, who wondered whether Trump’s actions truly reflect his personality or are part of “his shtick.”

One element Campbell said he does not understand, however, is Trump’s propensity for misstatements, particularly those that are easily refuted and don’t necessarily advance his image.

“I think people who are narcissist can be dishonest, but a lot of that dishonesty is in the service of themselves,” Campbell said. “Why, when there's no upside, do you lie at all? Unless that's just your default position.”

That, more than the self-regard, is what unnerves the GOP bundler, who said he sees it as undermining his ability to tell donors what Trump would do if elected. “Lying for the sake of lying. You've got to watch out for those guys,” he said.

In any event, whether Trump’s narcissism is an actual clinical disorder, or not quite that severe, is probably a distinction without a difference, at least for American voters. At 70 years of age, Trump is unlikely to change -- and change is only possible if Trump desires it.

“When you have narcissistic personality disorder, you may not want to think that anything could be wrong -- doing so wouldn't fit with your self-image of power and perfection,” the Mayo Clinic narcissism web page says. “People with narcissistic personality disorder are most likely to seek treatment when they develop symptoms of depression -- often because of perceived criticisms or rejections.”

Editor's note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims -- 1.6 billion members of an entire religion -- from entering the U.S.