In the late 19th century, French psychologist slash physicist slash anthropologist Gustave LeBon came up with the idea that being part of a crowd turned normal people into barbarians. LeBon believed civilized men (for the most part) lost their will, control, and ability to reason when they became part of a crowd. This theory of “mob psychology” held sway for decades, and still appeals to our notion that crowds of people make us act crazy.

Much of LeBon’s research came from studying the far-right nationalism and anti-Semitism that swept France during that era. So do his theories of mob violence and loss of identity explain the violence at potential Republican presidential nominee Donald Trump’s political rallies?

Well, probably not. More likely than a loss of identity is a shift—from individual to collective. “People don’t lose control, but they begin to act with collective values,” says Stephen David Reicher, a sociologist and psychologist at the University of St. Andrews in Scotland who has studied violence among modern-day soccer hooligans, race rioters, and, this year, Trump supporters. “It’s not your individual fate that becomes important, but the fate of the group.”

That sense of collective identity, and the desire to protect it from outside threats, may explain the fist-fights, punching, and sporadic tussles between Trump supporters and protesters—many of whom are members of minority groups targeted by Trump’s campaign rhetoric. “In the crowd, the thing that is important is ‘are they one of us, or are they one of them?’ That someone becomes the other. They become the pure enemy,” says Reicher.

The Wisdom(?) of the Crowd

Everything about the way Trump campaigns reinforces that self/other dynamic. That's what the slogan "Make America Great Again" whispers, after all.

“Trump rallies tell you something about the relationship among the followers and a strong leader. It is an America with a sense of anger and fear, fear that what you value will be taken away," says Reicher. "People are being told that what they value as Americans is under threat from all these forces, that for America to be great, these people have to be excluded—either thrown out from the rally or a by a wall being built.”

The rhetoric of the rallies, then, both reinforces and amplifies those feelings. People feel empowered to defend the collective—like the Trump supporter who sucker-punched a protester being led out of an event. “They are not hitting the person because they have a history with the other person. What they are doing, in a perverse way, is they are acting for the group,” Reicher says. “It’s a very dangerous cocktail.”

People are being told that what they value as Americans is under threat from all these forces, that for America to be great, these people have to be excluded. Stephen David Reicher, University of St. Andrews

And what of the protesters? Are they practicing free speech or provoking trouble? That's a tough one, because by some lights, protestors trying to shout down Trump are using some of the same methods used on college campuses to muffle unpopular speakers. “The attitude is if you violate my values, you won’t get to speak,” says Jonathan Haidt, a social psychologist at the New York University Stern School of Business.

In fact, Trump has blamed supporters of Democratic presidential candidate Bernie Sanders and the liberal group MoveOn for trouble at the rallies. “Of course they hate Trump and what he stands for,” Haidt says. “But what gives them the right to disrupt, interrupt and shut down a political event? If they do that at a Trump rally, are they surprised that people will try to hit them?”

Follow the Follower

As for Trump, its likely that he’s also feeding off the energy of the crowd, as Maggie Koerth-Baker pointed out in a fascinating piece at FiveThirtyEight. The technical term is “emotional contagion,” the same kind of effect that occurs at big football games, comedy clubs, and political rallies. People tend to mimic the behavior of those nearby, according to Stefanie Johnson, a management professor at the University of Colorado Denver. “There is evidence that emotional contagion flows from followers to leaders,” says Johnson, who has looked at this effect in her research. “It reinforces his energy and confidence. The more people are cheering, it makes sense that you are audibly yelling and reinforcing the power dynamic.”

The downside of this feedback loop between leader and follower is that people tend to make worse decisions when they are in a positive emotional state. Johnson notes that’s how salespeople work, getting the client in a good mood before they make a deal. “You can get people fired up and lot of serotonin going through their body, and they will be less critical about what he has to say,” Johnson says.

All that energy is like a pro wrestling match. “It’s about connecting with your audience,” says Patrick Stewart (not this one), a political scientist at the University of Arkansas. “It’s not what you say, but how you say it. He is saying things in such a manner that he is able to pull energy off the crowd. It’s a feed-forward mechanism. The problem is that his message is about anger, and anger vents itself.”

An apt comparison. Trump has a long history of involvement with pro wrestling. Maybe that's what makes him so hard to take to the mat.