Was Adolf Hitler a psychopath? Would he meet the criteria established by modern psychiatry? These were the questions invariably raised by audiences in Germany when I would give talks there about my 2012 book The Wisdom of Psychopaths. Fortunately, I was in a position to answer them with data. In an ongoing study, I had been asking the official biographers of prominent historical figures to fill out, on their subject's behalf, an abbreviated version of the Psychopathic Personality Inventory–Revised (PPI-R). This short psychometric test uses 56 questions to quantify a person's psychopathic personality traits.

The Führer, predictably, scored very high. What was surprising—and of some consolation to my German audiences—was that so did British prime minister Winston Churchill. Although Hitler's scores suggested that he was a hole-in-one psychopath, the numbers I collected for Churchill—one of the most celebrated figures ever to grace the world political stage—put him, too, solidly on the green. What did that say about politicians in general? If one of the all-time greats scores high on the psychopathic spectrum, might not many lesser luminaries lie there as well?

Now seems like a particularly good time to consider this issue. The U.S. presidential race has brought a host of personalities to the fairway, so to speak. The so-called Goldwater rule, part of the American Psychiatric Association's ethical guidelines, deems it unethical for psychiatrists to comment on an individual's mental state without examining him or her in person. (Indeed, the rule came about because in the 1960s, a now defunct magazine called Fact polled clinicians about whether Senator Barry Goldwater was fit for the presidency.) But from the media this election cycle, there has been no shortage of armchair diagnoses declaring several of the front-runners to be narcissists, megalomaniacs or psychopaths.

Are any of the candidates who have thrown their hat into the race really psychopaths? The label is far from one-size-fits-all. Although for most people it brings to mind serial killers such as Ted Bundy and Jeffrey Dahmer, experts use the term specifically to refer to individuals with a distinct subset of personality characteristics, among them ruthlessness, fearlessness, self-confidence, superficial charm, charisma, dishonesty, and core deficits in empathy and conscience. And while no one likes a heartless liar, the fact is that none of these traits in and of themselves presents a serious challenge to mental health. Instead what distinguishes the cold-blooded murderer from a psychopathic president is a question of context and degree. As with any personality dimension, resting levels of psychopathic characteristics vary. Using measures such as the PPI-R, researchers can conduct fine-grained analyses of these different components to uncover potentially toxic or helpful combinations—mixes that assist or derail the people who possess them.

Several studies have now placed past U.S. presidents and historical leaders under this microscope, revealing intriguing patterns. My own research has found that there are particular psychopathic traits that can benefit leaders enormously and others that lead to disaster in office. Recently I turned my attention to men and women vying for the U.S. presidency, who were, at the time I was writing this article: Hillary Clinton, Ted Cruz, Bernie Sanders and Donald Trump. In a new study, I assessed their psychopathic traits in much the same way I analyzed Hitler and Churchill. My results, described below, may give U.S. voters something to think about come November.

Will the Real Psychopath Please Step Forward?

To understand psychopathy better, imagine a personality “mixing desk” on which its hallmark traits, as measured by the PPI-R, consist of a hodgepodge of knobs and sliders. It would feature eight dials grouped across three different regions of the console. Though disputed by some scholars, one area would be labeled Fearless Dominance and include three components: Social Influence, Fearlessness and Stress Immunity, which are all self-explanatory. Another section, called Self-Centered Impulsivity, would feature four traits: Machiavellian Self-Interest, Rebellious Nonconformity, Blame Externalization and Carefree Nonplanfulness (a devil-may-care attitude toward the future). The third region would have a single dial: Coldheartedness.

If you could twiddle these controls in various combinations and see the results, you would soon arrive at two conclusions. First, there is no correct setting that defines all psychopaths. Depending on the timing and circumstances, individuals will constantly dial these traits up or down in search of the most effective alignment. And second, some jobs and professions—including management roles, business, law, the military, emergency services and surgery—demand that some of these dials are always cranked up a little higher than average. In general, high-risk, high-status positions place a premium on qualities such as decisiveness, mental toughness and emotional detachment—all of which are made easier by high settings on certain psychopathic qualities.

What specific mix serves as a psychological booster rocket in politics? To begin to find out, I conducted interviews with a number of British politicians and political commentators—from members of the House of Lords, to local elected officials, to well-known radio and TV anchors. They all deemed a few key traits to be indispensable for any politician. Foremost, they agreed that politicians must be able to make difficult decisions under considerable pressure. They need to be able to juggle many multifaceted crises, ranging from the threats posed by rogue nations to those caused by natural disasters. They have to be willing to send their country's young people to war in the certain knowledge that some will lose their lives. And they need excellent self-presentation skills and superficial charm—specifically, the ability to feign empathy even if they do not feel it. As Teddy Roosevelt once said: “The most successful politician is he who says what the people are thinking most often and in the loudest voice.” (Indeed, some observers credit the rise of Donald Trump to precisely this, at least among a portion of the electorate.)

Finally, the politicians I interviewed noted that even to run for office, politicians need supreme self-confidence. It then takes that same kind of Teflon-coated self-belief and unrelenting focus to implement policy. Dealing with opponents often calls for considerable ruthlessness and mental toughness. As one senior British politician told me: “The only way to tell who's stabbing you in the back in politics is to see their reflection in the eyes of the person who's stabbing you from the front!”

The picture of an ideal candidate that emerged from this survey was one of a charming, persuasive, self-confident individual who can be ruthless when necessary and who is also heat-resistant: he or she can maintain focus, keep a cool head and perform under fire. In terms of our personality mixing desk, the best setting would be “high” on all the Fearless Dominance dials, variable for the Coldheartedness dial and low for the Self-Centered Impulsivity dials. Put another way, politics came out as a profession in which an official consignment of legalized, precision-engineered psychopathy would come in rather handy.

Our Fearless Leaders

Several years ago psychologist Scott O. Lilienfeld of Emory University, who co-developed the Psychopathic Personality Inventory and is a Scientific American Mind advisory board member, joined psychologists Steven Rubenzer, Thomas Faschingbauer and others in an intriguing collaboration. First, researchers handed out the latest iteration of the NEO Personality Inventory, which assesses the so-called big five personality traits, to biographers of, or experts on, every U.S. president up to and including George W. Bush. Just as in my study, these experts used their in-depth knowledge of their subjects to answer on the presidents' behalf. Based on these responses, Lilienfeld then extrapolated to what extent each president exhibited various psychopathic character traits. From these data, I subsequently created two top-10 lists, ranking the presidents' scores in Fearless Dominance and Self-Centered Impulsivity [see box below].

How Presidents Rank in Psychopathy

Psychologists asked presidential biographers and scholars to fill out a standard personality assessment on behalf of their subjects. Based on the answers, the researchers calculated how high each president might score on measures of psychopathy. The results shown here rank all presidents up to George W. Bush by total score. Those listed in blue were among the top-10 scorers in Fearless Dominance traits of psychopathy, which are associated with successful leaders. Those listed in red ranked in the top 10 for psychopathic traits known collectively as Self-Centered Impulsivity, which are linked to less success. Four presidents, in boldfaced black, made both top-10 lists. The numbers in parentheses indicate position on the two lists. Credit: Eddie Guy/Getty Images

The results could not have been clearer. Similar to what I surmised from my survey of British politicians, higher settings on the Fearless Dominance dials were associated with higher ratings of presidential performance, leadership, persuasiveness, crisis management, perceived standing on the world stage and congressional relations. They were also linked to a number of more objective indicators of a president's performance, such as how many new projects he initiated. In contrast, higher settings on the Self-Centered Impulsivity dials were associated with indicators of an insalubrious interpersonal style—such as invoking congressional impeachment resolutions, tolerating unethical behavior in subordinates and having an unsavory reputation in general.

The findings also confirmed that biographers respond accurately enough to measures such as the PPI-R to reliably evaluate historical figures. For example, it is interesting to note that historians and political scientists consistently rate the two Roosevelts among the top-five greatest American presidents of all time, and in keeping with that assessment, they appear first and third on the Fearless Dominance top-10 list and are absent from the Self-Centered Impulsivity list. (Talk of Fearless Dominance: Teddy Roosevelt, after his 1912 electoral loss to Woodrow Wilson, set about exploring a previously uncharted tributary of the Amazon River, complete with piranhas, rapids and indigenous people bearing poison-tipped arrows!) In contrast, Andrew Johnson and Richard Nixon, who both feature on the Self-Centered Impulsivity top 10 but not on the Fearless Dominance list, are frequently cited among the worst.

My own ongoing study of historical figures is yielding similar profiles among the great, the good and the not so good [see box below]. As with the full version of the PPI-R, the short version does not have a cutoff score at which nonpsychopaths end and psychopaths begin. Instead it represents scores as percentiles of normative response patterns found across the general population. So to put my results in context, it is useful to know the scores associated with the top 20 percent (or upper quintile) of the evaluated subjects for its various traits.

Psychopathic Leader Board

The author asked biographers of historical figures to fill out the short form of the Psychopathic Personality Inventory–Revised (PPI-R) for their subjects. The table below reveals each subject's scores for psychopathy's eight component traits: social influence (SI), fearlessness (F) and stress immunity (STI), referred to as Fearless Dominance traits; Machiavellian Egocentricity (ME), Rebellious Nonconformity (RN), Blame Externalization (BE) and Carefree Nonplanfulness (CN), called Self-Centered Impulsivity traits; and Coldheartedness (C). Scores adding to the top 20 percent in the three major dimensions are highlighted. In another analysis, the author asked a seasoned political reporter to complete the PPI-R on behalf of contenders in the U.S. presidential race (bottom). Credit: Eddie Guy/Getty Images

Among men, that means that if an individual scores in the upper quintile across the three broader dimensions (that is, 68 or above for Fearless Dominance, 69 or above for Self-Centered Impulsivity, and 18 or above for Coldheartedness), he would weigh in with a minimum total score of 155. For women, the same 80th percentile watermark falls a little lower at 62.4 for Fearless Dominance, 62 for Self-Centered Impulsivity and 15 for Coldheartedness, for a total of 139.4.

In my list of leaders, everyone from Emperor Nero and above—including Jesus and Saint Paul—has a notably high total score and a top quintile finish on at least one of the three dimensions. British prime minister Margaret Thatcher falls just short of this distinction. If, however, you consider the scores broken down by dimension, you do find that some esteemed leaders land below the top quintile. Both George Washington and Abraham Lincoln are high on Fearless Dominance but low in Self-Centered Impulsivity and so come out with relatively modest total scores. In short, they have all the “positive” aspects of a psychopathic personality—affording them mental toughness, social influence and boldness—with none of the negative characteristics, which manifest as impulsivity, egocentrism and insubordination. In contrast, Hitler had all the “bad” aspects of psychopathy and fewer of the “good” ones.

The 2016 Race

To evaluate the top candidates in the U.S. presidential race, I contacted one of the BBC's most respected and seasoned American political news anchors, whom I assured complete anonymity, and asked this individual to fill out the PPI-R short form on behalf of the four leading contenders at the time—Clinton, Cruz, Sanders and Trump. In each case, this anchor answered the questions by drawing on personal firsthand experiences with the candidates, as well as expert media analysis and dispassionate general impressions.

When the results were tallied, Trump trumped the rest of the field, achieving a total psychopathy score in league with Hitler and Idi Amin. Of particular note, he outscored the other three contenders in the Fearless Dominance dimension, associated with successful presidencies. At the same time, however, his “negative” psychopathic ratings were also higher than the other three candidates. Across all eight psychopathic traits, Cruz ran pretty much neck and neck with his Republican rival—but lost ground when it came to Carefree Nonplanfulness and Social Influence: in other words, his scores suggested he is less impulsive and less persuasive than Trump. In summary, the comparison between the two did not prove a knockout for Trump, but if it were a boxing match, he would have won a unanimous points decision with Cruz still on his feet at the final bell.

Among the Democratic contenders, Clinton and Sanders were fairly evenly matched on “positive” psychopathic traits—both scoring high on Social Influence and in the middle of the road on the rest. That said, the two diverged markedly on “negative” psychopathic characteristics, with Clinton's higher tally forming the basis of her significantly higher total score. At 152, Hillary surged a full 16 points higher than Thatcher, the U.K.'s only female prime minister. Allowing for the gender differences in percentile cutoffs, her score was more on par with Trump's.

“A leader takes people where they want to go. A great leader takes people where they don't necessarily want to go but ought to be,” said Rosalynn Carter, wife of Jimmy Carter. The quote suggests that this first lady had some intuitive grasp of the idea that great political leadership entails cranking up some psychopathic dials on our personality mixing desk—those associated with fearlessness and dominance—while turning down the ones associated with self-centeredness and impulsivity. So far the research backs her up.

The Price of Greatness

What about leadership in nonpolitical spheres? In 2014 Lilienfeld and I, along with our colleagues, conducted a study that provided the first published data indicating a direct link between job status and psychopathic personality characteristics, drawing on an Internet-based survey of nearly 3,400 people. Specifically, we found that higher total scores on the short form of the PPI-R correlated positively, though modestly, with holding leadership and management positions. The association was significantly stronger for those attributes related to Fearless Dominance. We also found that people in high-risk occupations, such as police officers and firefighters, had much higher scores on all three PPI-R variables. Taken together, these studies support a particular view of what makes for an effective leader. Politicians and executives alike may not all be psychopaths (although some of them, of course, may well be). On the other hand, certain psychopathic traits—including mental toughness, social influence and fearlessness—do appear to be very useful in leadership roles and can help leaders to find considerable success.

These very same traits certainly helped Churchill. On July 3, 1940, early in World War II, he faced a standoff with the French at the port of Mers-el-Kébir in North Africa. In response to the Franco-German armistice of June 22, he dispatched a British task force to demand the surrender of the French battleships stationed there. The task force offered the French admiral three options to prevent the Germans from seizing his vessels: continue fighting the Germans; proceed under escort to a British port for repatriation after the war; or sail to a French safe haven in the West Indies. If he failed to comply, the British navy would scuttle the fleet.

The story does not end well. Churchill's brutal assault cost some 1,300 French sailors their lives. It was ruthless. It was fearless. And boy, was it decisive. It was also a political game changer. The indomitable resolve and unflinching fighting spirit demonstrated that day impressed Franklin D. Roosevelt and proved to be a major influence on the American decision to join forces with the Allies. The next U.S. president will also be poised to redirect world history. To make the right moves in a dangerous world, one can only hope that he or she possesses a similarly effective mix of psychopathic traits.