Populist rhetoric is widespread in the United States. In a widely aired campaign ad from before the 2016 election, candidate Donald Trump said, “Our movement is about replacing a failed and corrupt political establishment with a new government controlled by you, the American people.” A few years later, after Trump had become president, Sen. Bernie Sanders (I-Vt.) said at a Washington Post Live event: “A lot of working-class people out there voted for Trump, in a sense, because they gave up on the political establishment. Well, I, long time ago, gave up on the political establishment.” Later on, he continued: “I am prepared to take on the political establishment, to take on the corporate establishment, and stand up for the working class of this country.”

Populist rhetoric like this pits the good virtuous people against a corrupt and condescending political elite. It’s used by politicians of all ideological colors and can be a fruitful electoral strategy. It certainly contributed to Trump’s electoral success. And over the past two decades in Europe, populist parties have more than tripled their support. By now, about 1 in every 4 Europeans votes populist.

But to whom, exactly, does populist rhetoric appeal? Research finds that populist voters do not have much in common — at least not along traditional political lines. Those who vote for populists are often portrayed as having suffered economically from globalization. But no evidence exists that, on average, supporters of populist parties hold lower socioeconomic positions than those who do not support such parties.

Moreover, populist voters don’t necessarily share ideological positions or ideas about policies. Those who support populists can be politically left or right, progressive or conservative, multiculturalist or nativist, pro- or anti-LGBT rights, Euroskeptic or in favor of European unification.

Here’s how we did our research

In a recent study, we found that supporters of populists do have something in common: their personalities. Psychologists distinguish among five general traits that determine our personalities: openness to experience, extroversion, neuroticism, conscientiousness and agreeableness. This last personality trait — agreeableness — is what matters when it comes to populism.

Those who score high on agreeableness tend to trust others and to be modest, tolerant and cooperative. Those who score low are egoistic, cynical, distrustful and inclined to believe in conspiracy theories. Such low scorers on agreeableness can be highly susceptible to the populist anti-establishment message, because a message of distrust toward the political elite matches with their own cynical personalities.

Our research provides strong support for this expectation. For a first study we collected, combined and analyzed 13 publicly available data sets, representing nationally representative surveys from eight countries and three continents. All samples included items measuring personality traits and voting behavior. The results are striking: In all cases, we find that those who score low on agreeableness are more likely to support populists.

To find out whether it is the actual populist message that does the trick, we also conducted an online experiment. Data were collected by Survey Sampling International in July 2016, and we have a diverse sample of the U.S. population, consisting of 869 people. In it, we asked respondents to participate in a series of “elections” in which they had to choose between two fictitious political candidates. In each round, we randomly assigned ideological attributes to each politician.

Most important, a candidate could be either pro-establishment (“The House of Representatives is mostly full of honest and hard-working people who care about ordinary Americans”) or anti-establishment (“The House of Representatives is mostly full of Washington insiders who only care about themselves”).

The results clearly show that those who score low on agreeableness are more likely to choose an anti-establishment candidate over a pro-establishment politician. Interestingly, we do not find this to be the case with other messages, such as those emphasizing the centrality and virtuosity of the people or those opposing immigration. This suggests that those low on the personality trait “agreeableness” particularly respond to an anti-establishment message.

Other messages matter in other ways. We found, for instance, that an anti-immigrant message also attracts certain kinds of people: those who score high on authoritarianism. That’s not surprising, as many scholars have found that authoritarianism is linked to support for populist leaders.

In other words, different messages appeal to those with different personality traits — which means that politicians like Trump use various messages to attract different personality types. Of course, that’s true for all politicians. It’s not just populists who combine different messages to appeal to different kinds of people. What our findings reveal is that those messages appeal not just along familiar demographic lines like class, region or religion, but also by personality traits.

What does this all mean for democracies?

Contrary to what many people think, disagreeableness is not necessarily something negative. It’s a quality linked with an increased tendency to protest, speak up at public meetings and listen to different political opinions. And of course, critiques of the establishment can be functional and healthy for democracies. What makes some populists truly controversial are their xenophobic ideologies.

Bert N. Bakker (@bnbakker) is an assistant professor of political communication at the University of Amsterdam.

Matthijs Rooduijn (@mrooduijn) is an assistant professor of political science at the University of Amsterdam.

Gijs Schumacher (@gijsschumacher) is an associate professor of political science at the University of Amsterdam.