British newspapers tout the results of last week’s election. (Daniel Sorabji/AFP via Getty Images)

Last week’s general election in Britain highlighted a paradox: While the 2016 Brexit referendum reflected a rise in populist sentiment, the conservative leader who emerged, Theresa May, was a seasoned, establishment politician (who, for now, remains leader even though she has lost her parliamentary majority).

While populism is on the rise, the wave of newly elected leaders in 2016 and 2017 are a varied bunch that includes the politically experienced May and Moon Jae-in of South Korea, the outsider globalist Emmanuel Macron of France, and populist outsiders such as President Trump in the United States and Rodrigo Duterte in the Philippines. All took office facing pressing and important foreign policy choices for their countries.

So what makes these leaders tick? Does the psychology of populist leaders differ from that of others? Will political institutions and underlying interests keep these leaders in check, so that their foreign policies end up looking more or less the same as that of their establishment counterparts?

For decades, most political theories tended to assume that people were rational, which suggested that it didn’t much matter exactly who held power. Of course, psychologists have known for a long time that this assumption wasn’t always true, but it was difficult to study top decision-makers to draw general conclusions.

But a revolution has been underway in the behavioral sciences, rooted in psychology, that is improving our ability to link the attributes of individual people to real-world outcomes such as war and peace. A clutch of new studies, some of which are collected together in a new special issue of the journal International Organization, offer some fresh examples of how we can better understand how individuals matter in international politics. Here are three examples.

1. Leaders and the public are strongly affected by emotion.

Many leaders have used strong emotional appeals to stir support. Populist politicians who ride waves of public discontent into power are particularly keen to show they can change the system, making them perhaps more impatient to use emotional appeals than seasoned politicians working inside party machines.

Take one example: In survey experiments on a sample of the U.S. public, individuals with more intense national attachments are more likely to attribute malignant intentions to countries they already dislike and benign intentions to those they like, even when told that the countries engage in exactly the same behavior. Politicians, perhaps especially of the populist stripe, can mobilize and mute such sentiments — in effect, shaping national preferences.

That may help explain why some prominent Republicans have sharply changed their views of Russia despite the fact that Putin’s behavior has become more rather than less challenging. This major shift in U.S. policy may be less a rational strategic response to the situation than an emotional one.

Emotion can also affect the choices leaders make once in power. How people respond to foreign threats and opportunities may even have deep biochemical roots. New tools have made it is possible to measure these kinds of emotional responses. When emotions are aroused — a state that can be measured in the laboratory with probes that test how the skin conducts electricity — long-term calculations about when to stand firm and when to compromise with others, such as foreign powers, tend to go out the window.

These emotional reactions lead people to favor outcomes — such as war or diplomatic squabbles — that can generate gratuitous conflict with countries that are easy to push around. But the pressures of conflict can weaken a leader’s resolve when dealing with rising powers at times when it is important to hold the line. Research shows that the opposite would be better. Nations should make friends with parties whose interests are aligned with their own — but should stand firm against rising powers, because doing so will be even harder in the future. Perhaps these emotional motives explain why President Trump is finding it easier to pick fights that are not necessary — for example, with Canada and Germany — while avoiding those that involve more risks, such as those that may loom with both China and Russia.

2. Populist leaders are impatient.

Populists are not a patient lot. They know their time in power could be fleeting, and their supporters are passionate for quick change. But patience matters because it is related to how people evaluate costs and benefits.

Even when facing identical situations, different kinds of people construct very different mental maps of the costs of war. Impatient people are more sensitive to war casualties, which are paid in the short term; those who are more patient are more willing to pay these human costs in return for the long-run benefits of “staying the course.” The core of those differences may have less to do with conceptions of the national interest than with psychological traits that make some leaders and segments of the public persistent in war and crisis while others “cut and run.” There are obvious implications for continued U.S. commitment in Afghanistan and Iraq.

3. Knowledge and experience matter.

One theme in this wave of research is that knowledge and experience matter. Many analysts of trade policy are puzzled to see the Trump administration abandon the Trans-Pacific Partnership and launch a review that might abandon the North American Free Trade Agreement, in part because those campaign promises appealed to many in Trump’s base. Yet many studies show that most voters do not probably understand the economic consequences of such protectionism. Interestingly, new research shows that giving people information about economics can bring their trade policy preferences closer in line with their economic interests.

Experience also matters for leaders themselves. Inexperience, a virtue to voters who want change, can be dangerous for leaders. Unseasoned leaders are less able to monitor their advisers, question assumptions and plans, and diversify advice. They don’t have good mental models to help them reason through situations they’ve never seen before. Untested ideas get a more serious hearing. The result includes mixed signals, as we have seen on issues ranging from the White House’s response to Brexit, the alienation of allies, and how to handle North Korea.

The new research on leaders is not all gloomy. Emotion, for example, can push people toward cooperation and adherence to international rules and norms. Research on German politicians has shown that some political elites focus on their roles as “dutiful compliers,” always willing to follow the rules, motivated by strong identification with the European ideal. That kind of logic may be one of Europe’s defenses against populism.

While leaders aren’t all powerful, they matter a lot — especially when their personal proclivities lead them to push for rapid change and visible, quick wins, rather than the slow, hard spadework of quiet diplomacy. Thanks to a true collaboration across the social sciences, we know much more about how emotional, impatient leaders are likely to act, and how democratic publics are likely to respond.

Emilie M. Hafner-Burton is the John D. and Catherine T. MacArthur Professor of International Justice and Human Rights at the School of Global Policy & Strategy (GPS) at the University of California at San Diego.

Stephan Haggard is the Lawrence and Sallye Krause Professor of Korea-Pacific Studies and director of the Korea-Pacific program at GPS at the University of California at San Diego. 

David A. Lake is the Jerri-Ann and Gary E. Jacobs Professor of Social Sciences and Distinguished Professor of Political Science at the University of California at San Diego.

David G. Victor is professor of international relations at GPS at the University of California at San Diego, and co-head of the Brookings Institution Initiative on Energy and Climate.