President Donald Trump has shown signs of a mental health disorder and he should be evaluated and diagnosed by mental health professionals, according to Stanford University psychology Professor Emeritus Philip Zimbardo.

Zimbardo co-authored a chapter in the book, "The Dangerous Case of Donald Trump," published last October. The book included chapters from 27 mental health clinicians assessing, from a distance, the behavior and public statements of the president.

Zimbardo's chapter was on what is called "present hedonism."

"Present hedonism is characterized as living in the moment with no interest in the past or the future," Zimbardo said in an email interview last week. "All decisions are made on the spur of the moment without ever considering their future consequences and without considering whether they were effective in the past."

The president, Zimbardo added, has exhibited the most extreme signs of present hedonism he's ever seen.

Zimbardo said that his concerns about Trump's mental health have increased since "Dangerous Case" was published.

"He is as impaired as I thought he would be, and more," Zimbardo told the Weekly. "I did not expect the sharp cognitive decline as well as neurological symptoms, primitive grasping of a water cup and slurred speech, as we have seen, in addition to psychological symptoms."

Zimbardo also spoke to the president's tendency to exaggerate or apparently lie.

"He shows a need to fabricate his reality, not just for his base but also for himself and cannot refrain from entering into an attack mode," Zimbardo said. "He cannot help himself because this is the structure of his pathology."

Zimbardo added: "An evaluation will help confirm and assess how deeply his impairment goes. It would allow us to formulate a treatment plan, as well as to have an understanding of what he is and is not capable of."

Part of what Zimbardo calls the president's pathology is exhibited in his constant use of Twitter to express his opinions and, most often, his displeasure.

"In the last 380 days since in his inauguration, Trump has made 4,776 tweets, which averages out to 12.6 tweets every day and night," Zimbardo said. "Some are filled with garbled inconsistencies, attacks on his perceived enemies, and glorification of his imagined achievements."

The question of Trump's mental health has been openly discussed since the book "Fire and Fury" by Michael Wolff, about the Trump presidency, was published last month. The book purports that many in the White House have questions about the mental stability of the president. Wolff's reporting methods have themselves become a topic of concern among journalists, however, because of his lack of direct sourcing.

The Atlantic magazine's website reported in December that about a dozen Democratic lawmakers invited the editor of "Dangerous Case," Yale University psychiatry Professor Bandy Lee, in for closed-door talks. Those meetings are continuing, Lee has confirmed.

"Dangerous Case" was written conscious of the American Psychiatric Association's Goldwater Rule, established in 1973, which stipulates that therapists should not comment on the mental health of someone they have not personally evaluated.

The Goldwater Rule is a pillar of ethics in the world of psychiatrists. But it amounts to what Lee called a "silencing mechanism" preventing therapists who wish to from speaking out. (Lee herself resigned from the American Psychiatric Association a decade ago over what she called growing ties between the group and the pharmaceutical industry.)

"We are trying to abide by the Goldwater Rule ... not to diagnose but to educate the public in general," Lee said in a recent email. "We are merely stating that Mr. Trump is dangerous and needs an evaluation, which in turn will yield diagnoses, if any."

The American Psychological Association, which Zimbardo belongs to, has something similar to the American Psychiatric Association's Goldwater Rule. In its "Bases of Assessment," Standard 9.01 states that "one should not assess individuals without direct contact."

When informed that his statements to a reporter could be construed as a violation of the American Psychological Association's "Bases of Assessments," Zimbardo replied in a short email: "I don't care."

"A psychiatrist who disregards the basic procedures of diagnosis and treatment deserves reprimand," Lee wrote in the book's prologue. "However, the public trust is also violated if the profession fails in its duty to alert the public when a person who holds the power of life and death over all of us shows signs of clear, dangerous mental impairment."

Last March 16 and again on Oct. 6, the American Psychiatric Association issued reaffirmations of the Goldwater Rule to its members. The Oct. 6 reiteration occurred when "Dangerous Case" was published and specifically referred to a concept among clinicians as "duty to warn," when a therapist believes it is necessary to break the bonds of confidentiality when a patient exhibits signs of being a danger to himself, herself or to others.

The idea for the book was born out of a meeting on April 20 at the Yale School of Medicine organized by Lee and titled "Does professional responsibility include a duty to warn?" Lee convened respected, longtime colleagues in the field to discuss whether a situation involving a public figure could arise that would entail an ethical duty to speak out.

This is not the first public attempt of mental health professionals to cast their diagnostic eyes on Trump from a distance. The cover story in the June 2016 issue of Atlantic magazine, written by Dan B. Adams, a Northwestern University psychology professor, also raised questions about then-candidate Trump's mental health.

Editor's note: The original version of this article has been edited to correct information about the April meeting at Yale and also Lee's characterization of the Goldwater Rule. Palo Alto Online regrets the errors.