“You know, if it gets a little boring, if I see people starting to sort of, maybe thinking about leaving, I can sort of tell the audience, I just say, ‘We will build the wall!’ and they go nuts.” — Donald Trump speaking to New York Times editorial writers in January.

The psychological relationship between Trump and his audience looks, at first glance, to be exclusively top down. Trump speaks, and then the masses erupt. That certainly seems to be how Hillary Clinton, Bernie Sanders, Marco Rubio and John Kasich see it. All of them have accused Trump of inciting violence, and Kasich has said “there is no place for a national leader to prey on the fears of people.”

But there are hints, particularly in that New York Times quote, that something more complex is happening. As much as Trump shapes the feelings and behavior of his followers, it’s also probable that they are shaping him. The masses get bored, and then Trump erupts.

He isn’t alone. Psychologists who study emotion, behavior and social dynamics tell me that political rallies of all stripes almost certainly involve this sort of feedback loop. And they think so even though only two studies exist to document any evidence of it.

This proposed symbiotic relationship between leaders and followers is based on an idea called “emotional contagion” — our tendency to unconsciously mimic the outward expression of other people’s emotions (smiles, furrowed brows, leaning forward, etc.) until, inevitably, we begin to feel what they’re feeling. More than two decades of research by dozens of scientists has documented emotional contagion both in the lab and in real life.

It happens automatically. Johnson, a psychologist and assistant professor at the University of Colorado Boulder business school, studies emotional contagion because of the role it can play in building power relationships and corporate culture in the office. She said the dynamic also applies to politics. Think of the way you could be pulled in by your favorite candidate at a rally and by the mood of the rest of the audience. Suddenly, you’re caught up in collective feelings of hope or anger, excitement or fear. It can happen in smaller settings as well, as when you go out for coffee with an anxious friend and come away feeling anxious yourself, said Sigal Barsade, a psychologist and professor at the Wharton School.

Almost all the research treats the crowd as an object acted upon, its emotions molded by a leader — or sometimes by its own members, like an emotional version of the Wave. I spoke with four scientists, including Elaine Hatfield, a social psychologist and professor at the University of Hawaii, an originator of the concept of emotional contagion. They could point to only two studies that considered how followers might incite emotions in their leader.

In one, from 1990, researchers studied interactions between people designated as “teachers” and “learners.” They expected to find that emotional contagion flowed downstream from the teacher to the taught. Instead, they discovered strong statistical evidence that the teachers were picking up emotional cues from their students. The other, from 2006, involved 48 groups of three — two designated followers and one leader. The groups were given the task of constructing a model car; secretly, the followers were told to express either strongly positive or strongly negative emotions about the process. The researchers documented mood by comparing the self-reports of the leaders, the reports of the followers about how they thought the leaders felt, and the reports of a third-party observer. They found that the followers’ assigned mood correlated strongly with the mood the leader would end up expressing and feeling.

Despite this paucity of evidence, all the scientists I spoke to assumed emotional contagion flows both ways — top down and bottom up. “It makes total sense,” Barsade told me. “If you’re a speaker in front of a roaring crowd, the emotion you’re going to feel back from that crowd is incredibly powerful. It’s largely automatic. You’d have to consciously regulate yourself to have it not happen.”

They all described the experience of a politician speaking to a crowd as a symbiotic feedback loop: The politician sets an emotional tone that is picked up by the crowd, which expresses its own emotional state that the politician responds to. On both sides, the emotional mimicry has an influence on behavioral choices. When Trump knows that he’s losing his audience and that talking about the wall will bring them back, the interaction could be seen as an expression of emotional contagion in action.

There’s a great example of this in FiveThirtyEight’s documentary on Howard Dean and his infamous scream. “I’d get out there and talk about policy and there was no adrenaline rush,” Dean said in the video. “And I really wanted that huge charge of being able to crank them all up and believe in themselves again and get enthusiastic. And I would succumb to that.” Dean blames his loss in the 2004 primary in part on this inability to moderate his emotions on the stump.

From this perspective, Trump’s use of violent rhetoric isn’t just something he’s forcing on an easily manipulated mob. They respond to him. But he also responds to them. And they build up each other’s feelings of excitement and anger.

Given the important role of bottom-up emotional contagion, why is it so little studied? Partly, Patrick Stewart, an associate professor of political science at the University of Arkansas, told me, it’s because politicians and other public speakers don’t want to be studied. But it’s also a function of our culture’s belief in the ideal that leaders have all the power, that they’re the ones running the show. “But it’s always a dialogue,” Stewart said. “Without the followers the leader is nothing.”

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