The president is a "narcissist." He is "paranoid." He is "bipolar."

No, not President Trump.

These labels were applied to Bill Clinton, Richard Nixon and Theodore Roosevelt, respectively. And the list goes on. John F. Kennedy had psychopathic traits, according to one academic study. And Abraham Lincoln apparently experienced suicidal depression.

"Many of our greatest politicians have had psychiatric vulnerabilities," says Ken Duckworth, a psychiatrist and medical director for the National Alliance on Mental Illness. But that didn't necessarily make them incompetent or unfit for office, he says.

So it's troubling that there have been so many armchair diagnoses of Trump in 2017, Duckworth says.

The most prominent of these came in the form of a book, The Dangerous Case of Donald Trump, written by 27 psychiatrists, psychologists and other mental health professionals. In separate essays, they argue that Trump exhibits "pathological narcissism," "unbridled and extreme present hedonism" and "delusional disorder," among other problems.

Some mental health professionals also signed an online petition saying that Trump "manifests a serious mental illness that renders him psychologically incapable of competently discharging the duties of President of the United States."

And many government officials and politicians have added their voices.

James Clapper, a former director of national intelligence, questioned Trump's "fitness to be in this office." Sen. Bob Corker, R-Tenn., said in August that Trump had not demonstrated the "stability" to be president. Shortly after that, Rep. Zoe Lofgren, D-Calif., issued a statement asking: "Has emotional disorder so impaired the president that he is unable to discharge his duties?"

Most psychologists and psychiatrists, though, have avoided public speculation about the president's mental health. One reason is that both the American Psychological Association and the American Psychiatric Association have policies saying it's unethical to diagnose public figures from afar.

Duckworth supports those policies and says many of the mental health professionals who are speaking out seem to have a political agenda. "When you don't agree with someone, it's not helpful to label them as having a psychiatric illness," he says.

Also, it's poor practice to label a person you've never personally examined, Duckworth says. "You are supposed to spend an hour and a half with a human being before you make a diagnosis, not just look at three Twitter rants and make a conclusion," he says.

Even if Trump does have a psychiatric disorder, that wouldn't set him apart from a long list of other U.S. presidents, says Dr. Marvin Swartz, head of the division of social and community psychiatry at Duke University.

Biographical information suggests that nearly half of the presidents from 1776 to 1974 met criteria for mental illness at some point in their lives, according to a 2006 study by Swartz and two colleagues. "But that doesn't mean they were incompetent or unable to do high-functioning tasks such as being president," Swartz says.

Depression was the most common problem, appearing to affect nearly a quarter of the presidents, including James Madison and Dwight D. Eisenhower. Thomas Jefferson, Ulysses S. Grant and Calvin Coolidge all appeared to have social phobia, an overwhelming anxiety about social situations and interactions with other people.

Many historians have described Richard Nixon as paranoid. But the Duke team found stronger evidence that Nixon had a serious drinking problem.

"The accounts of his alcohol abuse were disturbing," Swartz says, noting that Nixon's staff tried to make sure he didn't make decisions in the evenings. "Having to keep the nuclear codes away from the president after dinner is concerning."

Perhaps the best-documented mental illness in a president was Abraham Lincoln's depression.

During his 20s and 30s, the future president was "pushed into a real despair and was talking openly of suicide," says Joshua Wolf Shenk, who wrote the book Lincoln's Melancholy. "Lincoln himself said he wouldn't carry a knife with him for fear of what he might do with it."

Lincoln's depression eased for 15 years, then returned during his presidency as he oversaw a bloody and brutal war. He was so affected by the suffering that "he was weeping openly and saying things like, 'If there's a place worse than Hell, I'm in it,' " Shenk says.

Yet the president's emotional response did not undermine his ability to lead, Shenk says. And there is evidence that his early experience with depression made him "more tender and more resilient" during his time in power.

The public response to a complex, emotional president would almost certainly be much more negative today, Shenk says. "The modern concept of leadership is one that is very unforgiving of any kind of complexity or variation," he says.

For example, in 1972, when the public learned that Democratic vice presidential nominee Tom Eagleton had been hospitalized for depression, he was forced to quit the race. And in 1998, when Bill Clinton was mired in a sex scandal and facing impeachment, his staff assured reporters that the president was not seeking help from any mental health professional.

As for Trump, "he is obviously impulsive and has a personality style different than most presidents," Swartz says. But suggestions that a psychiatric disorder has made him incompetent or unfit have come primarily from "people who disapprove of his behavior," he says.

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