As a past president of the American Psychiatric Association, I feel strongly that my fellow psychiatrists, and any psychologists or therapists, should stop speculating publicly about President Trump’s mental fitness and stop trying to diagnose possible mental conditions based on their armchair observations.

It’s not that Mr. Trump’s mental fitness should not be evaluated — quite the contrary. All sitting presidents should be evaluated, though most presidential physical exams have included only cursory evaluations of their mental health. When President Trump undergoes his annual medical examination on Friday, his first since taking office, I hope that his assessments include the specific tests that could readily determine if he suffers from a neuropsychiatric condition that could explain his erratic behavior and undermine his ability to perform his duties.

But even if these tests are conducted, it is unlikely that we will learn the results. This would be unfortunate, because speculation about Mr. Trump’s mental fitness appears to be reaching its zenith. It is not just the odd behaviors that have become so common: his obsessive tweeting; his shocking, often contradictory statements; and his instances of confusion (for example, not recognizing Rudy Giuliani sitting across from him at a White House meeting or appearing not to remember the words to the national anthem at a sport event).

Now we have Michael Wolff’s book, “Fire and Fury,” in which the president’s own staff members question Mr. Trump’s stability and cognitive ability. In response to early accounts of the book, the president tweeted in defense of his mental capacities that “actually, throughout my life, my two greatest assets have been mental stability and being, like, really smart.”

Yet the reality is that, unless the president is properly evaluated, we have no real evidence to know with certainty if he has a mental disorder. And even if we did, we lack a clear constitutional standard for what severity of impairment would render him unfit to serve. History has shown us that former presidents have suffered conditions hampering their mental function while still in office, including Ronald Reagan, Calvin Coolidge and Woodrow Wilson. Consider the case of Reagan: He was eventually diagnosed with Alzheimer’s, but if he was beginning to show symptoms in his second term, as some believe he was, that did not preclude him from finishing his term.

The experiences of those presidents provide convincing evidence that, even if there weren’t a tsunami of speculation about Mr. Trump’s mental condition now, Congress should consider adopting policies to standardize, and to expand as needed, the scope of presidential medical exams to include neuropsychiatric assessments.

As I have written, disorders such as psychosis, dementia, depression and addiction commonly occur in people in the age range of presidents — and any of those, when severe enough, could damage a president’s ability to discharge his or her duties. The 25th Amendment provides a process for transferring power from presidents deemed incompetent. However, we still lack a defined process for applying the 25th Amendment to a president who will not voluntarily submit to an examination to evaluate mental competence. We also lack clear criteria for what behavior warrants an intervention and transfer of power to the vice president.

The 25th Amendment has been invoked only a handful of times since its ratification in 1967. But except during the Watergate scandal, these incidents mainly involved giving vice presidents the power of the presidency while the president was undergoing medical procedures that included general anesthesia.

There is another problem with the current debate over Mr. Trump’s mental condition: It assumes his behavior isn’t voluntary, and that his shocking or “unpresidential” conduct is a symptom of mental illness. This kind of thinking contributes to the stigmatization of mental illness. It’s entirely possible that he simply has certain personal qualities we don’t find ideal in a leader, like being a narcissistic bully who lacks basic civility and common courtesies. That he is, in a word, a jerk. But that alone does not make him mentally unfit to serve.

It’s also worth noting that when psychiatrists engage in clinical name calling about the president’s mental status without adequate evidence and proper evaluation, they are damaging the credibility of the entire field. Psychiatry has had a checkered past: Witness its collusion in Nazi eugenics policies, Soviet political repression and the involuntary confinement in mental hospitals of dissidents and religious groups in the People’s Republic of China. More than any other medical specialty, psychiatry is vulnerable to being exploited for partisan political purposes.

We can raise an index of suspicion, make back-seat observations of someone’s behavior to express our concerns and even speculate as to whether illness may be the underlying cause. But those observations, coming from physicians — even psychiatrists like myself — are merely public opinion. They are not reliable as evidence for definitive diagnosis and removal of a sitting president from office. Mr. Trump’s public behavior will never be enough for us to determine his mental fitness because a diagnosis requires a thorough and nonpartisan examination.

To put this matter to rest, either President Trump should voluntarily submit to a neuropsychiatric evaluation or mechanisms should be established to require him — and all future presidents — to do so.

Jeffrey A. Lieberman is the chairman of psychiatry at Columbia University College of Physicians and Surgeons and the author of “Shrinks: The Untold Story of Psychiatry.”

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