James Madison, John Quincy Adams and Franklin Pierce all suffered from major depressive disorders. Theodore Roosevelt was bipolar. So, too, was Lyndon Johnson. Woodrow Wilson suffered from a generalized anxiety disorder. If only we knew then what we think we know now.

It turns out that about half the presidents between George Washington and Richard M. Nixon suffered from some sort of psychiatric disorder. This is different from saying that you have to have a mental disorder to be president, which is an amateur’s irreverent observation, though perhaps open to clinical testing. The cases mentioned above were diagnosed by three members of the Department of Psychiatry at the Duke University Medical Center in North Carolina, and they’re not being playful. They’ve conducted the first psychiatric inventory of the presidency, and it’s a serious study.

The sheer volume of psychiatric disorders resident in the historical presidency is, at first blush, staggering. Most of us have given very little thought to the mental health of, say, Rutherford B. Hayes (major depressive disorder) or James Garfield (depression, again). But to realize that 10 presidents suffered from depression is to concentrate the mind on why it often seems so difficult for presidents to concentrate the mind.

In truth, there is a very important message in the three psychiatrists’ report, published this winter in the Journal of Nervous and Mental Disease. This study tells us that presidents are more vulnerable and less perfect than we sometimes think. It tells us that people with mental illness can be highly functional and highly successful. And, because the presidents suffer rates of mental illness roughly comparable to the general public, it reminds us that mental illness, especially depression, is more widespread than we sometimes acknowledge.

“These are ordinary people in some ways,” says Marvin S. Swartz, one of the Duke psychiatrists. “They are not immune to mental illness.”

This report may become irresistible fodder for political scientists of the Jay Leno and Jon Stewart schools, but if interpreted soberly it may be one of the most potent political tools the mental-health lobby has ever acquired. That lobby can now enlist Thomas Jefferson (social phobia, non-generalized), Abraham Lincoln (major depressive disorder, recurrent, with psychotic features) and Dwight D. Eisenhower (major depressive disorder) among those who suffered from mental illness. (Winston Churchill was an honorary American – a status conferred by Congress in 1963, the first time such a designation was made – and he, too, suffered from depression.)

Activists advocating programs for alcoholics can take heart, too. Ulysses S. Grant is probably the most famous alcoholic in American history, but not the only alcoholic president. Franklin Pierce suffered from alcohol dependence, and Nixon from alcohol abuse.

Presidents may not rule from the grave, but psychiatrists can still give rulings on men in the grave. In this case, the Duke investigators examined biographies, histories, medical studies and journals to find suggestions of psychiatric disorders. Then they applied this information against a strict rubric to evaluate whether they could reasonably conclude that an individual president suffered from mental problems.

Some presidents emerged perfectly healthy, mentally speaking, although as political analysts and not practitioners of psychiatric analysis we can say with confidence that there was nothing rational about how one of them, James Buchanan, let the country slip into civil war, or how another, John F. Kennedy, let himself slip into bed and compromising relationships with dozens of women while he was presiding over tense Cold War years.

On the other hand, Andrew Jackson was fiercely, almost maniacally, competitive, but completely healthy. I have long wondered whether William McKinley suffered from mental disorders, but his behavior might best be described as abiding devotion to a wife who herself suffered from debilitating headaches and seizures. He gets a clean bill of health from the Duke psychiatrists.

Some of the presidents, to be sure, came to office with a proclivity to mental disorder, only to find that the stress of office pushed them into illness. But some – Calvin Coolidge, Franklin Pierce – developed mental disorders after their sons died tragically, Coolidge’s from a bizarre toe infection after a blister developed during a tennis game, Pierce’s from a terrible train accident. “Neither president was able to commit himself effectively to the task of leadership following such tragic loss,” the psychiatrists write. “(T)raumatic bereavement may have left each one poorly equipped to discharge the demanding responsibilities of office.”

In many cases, presidents overcame mental disorders or mined their strengths of character to emerge as national leaders despite mental problems. “To contemporaries well acquainted with Madison, Hayes, Grant and Wilson,” the psychiatrists write, “it must have appeared that, as young men, these individuals were doing very little with their lives, with Grant, in particular, unable to hold down even the most simple employment on account of alcohol problems.”

The Duke team did not examine the presidents after Nixon, but it is reasonable to guess that they would have found that Gerald R. Ford and George H.W. Bush were exceedingly healthy psychologically. We know that Ronald Reagan suffered from Alzheimer’s late in life and perhaps even in the White House. George W. Bush has admitted freely that he abused alcohol in the years leading up to his 40th birthday. Bill Clinton exhibited colorful personal behavior before and during his presidency, but let’s leave it to the next study for a professional diagnosis.

All this is intriguing, but perhaps only as presidential prurience. But it is important information for two reasons quite apart from the tantalizing notion that William Howard Taft had a breathing-related sleep disorder or that Coolidge suffered from social phobia. (In the latter case, one reading of the man’s biography should be sufficient to convince even the most casual observer.)

The important implications of this study: There is no evidence that mental illness led to national catastrophe. (Indeed, it was a man with severe mental disorders who saved the nation during its gravest challenge, the Civil War.) And the prominence of mental illness in our most prominent citizens can only serve to diminish the stigma of psychological problems. In that regard, some of our presidents are serving their country long after having left office.