Donald Trump will be president of the United States of America, and the wielder of all the powers that the position contains. What many fear today is the power he will have to change people’s lives in dramatic and potentially harmful ways, especially if he follows through with campaign promises to deport undocumented immigrants, to ban Muslims from entering the United States, or sign a law that will take health insurance away from millions. He’ll have power to end lives with military campaigns and drone strikes.

Power gets into our heads. It changes us. Power can give us confidence to indulge in our base urges. It can make us less empathetic, more likely to see our own success in a positive light and harshly condemn failures in others.

“People who are pro-social are very pro-social when they have power; people who are more selfish are even more selfish”

And what many feared throughout Donald Trump’s campaign — a fear that now is much more acute — is what happens when a man who has a history of testing the bounds of his power or outright abusing it becomes president. What will such a man do with even more power?

As Michael Kraus, who studies the psychology of power at Yale, wrote recently at Quartz, power is only likely to magnify the negative characteristics in a man like Trump. But for an interesting reason: It’s not that power by itself is corrupting. It’s that “power simply brings our true nature out into the open,” Kraus writes.

In that light, investigations into Trump’s “true nature” — how he interacts with women and around employees, how he responds to failure, how he lies about contributions to charity, how he lies, seemingly compulsively, and on and on — matter.

They may matter as much as his policy proposals and his administration’s agenda. Because when a person is given more power, they become even more like themselves.

This is the way to think about how candidates will wield power: It isn’t necessarily corrupting — it’s freeing

Psychology defines power very simply: It’s our ability to influence others and the world. It’s accrued in so, so many ways: by the amount of money we have, by the social class we’re born into, by the force of our personalities and intellect, by the teams and institutions we associate with, and so on.

“Power is to humans and their relationships [what] energy is to physics,” Kraus says, paraphrasing Bertrand Russell.

The more powerful we are, the freer we are to act on our base desires. (Robert Caro came to this conclusion — power doesn’t corrupt, it reveals — in his biographies of Lyndon B. Johnson.)

When we’re not in a position of power, we’re constrained by social norms and expectations. We make decisions that don’t rock the boat; we’re maybe more polite; we’re less confident in our ideas.

“Power removes some of that,” Kraus says.

When those barriers are removed, the “true self” — meaning a person’s personality, the gut way they react to the world — is revealed. (Psychologists generally feel personality is a stable trait. Meaning the Trump personality we’ve seen is likely the one we’ll get.)

In his research, Kraus finds that when people feel powerful, they’ll behave more consistently, whether they’re among relatives or friends, whether they’re posting to Facebook or to a dating website. The context of the situation doesn’t get in the way of the self.

In the lab, Kraus and his colleagues can make participants feel powerful just by having them write essays about a time they felt powerful, or by having participants think of the less fortunate. Almost immediately, the change takes place.

“People who are pro-social are very pro-social when they have power; people who are more selfish are even more selfish when they have power,” Pamela Smith, a psychologist studying power at the University of California San Diego, says. Studies find that when people who are more altruistic are given power, they share more with other study participants. The opposite is true for those inclined to be selfish.

“Power magnifies your personality traits,” says Dacher Keltner, a psychologist who collaborates with Kraus and recently published The Power Paradox, a book outlining the psychological science of how we gain power and what it does to our minds. “Given that, we might want to find [candidates] who have balanced, moderate personality traits.”

That is, if you want a leader with balanced, moderate personality traits. As this election showed, there are plenty of Americans who’ll support Donald Trump, whose personality is bombastic.

Power nudges us to be a bit more self-serving

Power puts a magnifying glass to our personalities, but it also subtly influences all of us to become a bit more selfish. “We know power amplifies our more dangerous tendencies,” Keltner says. “It will make us behave in more irrational ways.”

In the book, Keltner writes about many studies that show the subtly sinister influence of power.

More powerful people are less empathetic, and are literally less able to read emotion in the eyes of others.

More powerful people are less likely to take the perspective of others. In one very simple but small experiment — only 57 subjects — participants were asked to draw the letter E on their foreheads. The participants who felt more powerful were less likely to draw the letter so that others could read it correctly. Here’s what I mean:

Powerful people are more self-serving. In an experiment, Keltner brought groups of three participants into the lab and had them play a game where one was given the role of the leader. He then brought out five cookies as a snack. “And indeed, the high-power participants were nearly twice as likely to grab a second cookie, with their peers looking on,” Keltner writes.

Powerful people, as measured by job status, are more likely to report that they’ve had an affair (which suggests that they either felt freer to engage in the action or felt less shame in admitting it). In other surveys, “people feeling powerful were more likely to say it’s okay to not pay taxes, and that there’s nothing wrong with over-reporting travel expenses or speeding on highways,” Keltner writes.

The powerful are also more prone to hypocrisy. One 2010 paper out of Northwestern and Tilburg universities found evidence that while powerful-feeling people judge others more harshly for breaking rules, they cut themselves some slack when they bend the rules. “People with power take what they want not only because they can do so without punishment, but also because they intuitively feel they are entitled to do so,” the paper concluded.

Past behavior may be more important than campaign behavior

There’s a good rule for determining who will be better at wielding power: Look at their past behavior, Kraus says. “I would pay far more attention to that than promises of what we’re going to do as a country at commercials and rallies.” (Again, “better” is subjective here. A great many Americans might like a leader with authoritarian tendencies.)

Look to the history of “them being deceitful, them being selfish, of not being fair,” Smith says. “If they claim, ‘I’m a changed person,’ look for evidence that they actually have changed. If this is something they were still doing last week, they are probably still that way.”

There is one bright spot in the research, however. Smith says when she runs lab studies where she makes people feel powerful, she finds it also increases feelings of responsibility. “There were no presidential candidates in our sample,” she notes, “but we find this nice association.”