What better time to gauge the emotional profile of Senator Bernie Sanders (I-Vt.), an avowed Socialist, than during his Labor Day speech to the AFL-CIO in New Hampshire? After all, the independent junior senator from Vermont, who’s running for the Democratic Party’s presidential nomination, has a website home page that focuses on economics and the working class. Creating jobs, raising wages, “taking on the enormous economic and political power of the billionaire class” is what Sanders says his campaign is all about.

Does he back up his heated words emotionally? You bet. On Labor Day, Sanders, as usual, comes out swinging. Literally. He uses a double-barreled hand gesture for emphasis — both hands clenched into fists and raised level with his head. Add a barrage of finger-pointing to drive home his resistance to the status quo, and you’ve got Sanders’s body language nailed.

But that’s just the obvious stuff. Sanders’s somewhat more subtle facial expressions also mark him as the angriest candidate in this year’s election cycle. When I facially coded all the candidates’ campaign launch speeches, more than half of Sanders’ address fell on the anger spectrum — from annoyed to frustrated to outraged.

Sanders registers anger far more than any other emotion. Watch how his chin thrusts upward during or between sentences, often as his lips press together. How tightly he presses them together is a barometer of whether an issue makes him merely frustrated or downright angry. Then round out the package with a furrowed brow and narrowed eyes.

It used to be that American presidential candidates obligingly smiled to the cameras and the crowds. It showed you were calm and cool, upbeat — a winner.

But not Sanders. Though he is attracting large crowds at campaign events, now as much as five times the size of former Secretary of State Hillary Clinton’s biggest audiences, it doesn’t get him to lighten up. Since he is insisting that he won’t be bought off by wealthy donors, he has pulled in contributions from more than 400,000 people. Yet that also doesn’t seem to soften his anger.

Sanders is succeeding beyond most political analysts’ expectations. The senator admits that he is “stunned” to have pulled even with Clinton in recent Iowa polls. He is ahead in New Hampshire — which, granted, is Vermont’s neighbor.

The amazing thing, however, is that, despite this success, Sanders appears to have gotten even angrier since his campaign launch. It’s almost as if he’s the candidate of wrath. It seems that his strong support might only have strengthened his resolve to continue his fight against the long odds and beat the “establishment.”

To understand that phenomenon, let’s examine what anger means and how it works. Of the seven core emotions — happiness, surprise, anger, fear, sadness, disgust and contempt — there are only two approach emotions: happiness and anger. To hug or to hit. In kicking-off his campaign, Sanders was occasionally happy. Now that’s gone. It’s been replaced by a desire to smack down those responsible for income and wealthy inequality, for a declining middle class, for big money dominating politics. This appears to have become the driving force behind Sanders’s campaign.

That figures. Anger is about wanting to be in control of your life and make progress. Sure, you can get angry because you’re confused and, therefore, don’t feel in control. But Sanders isn’t confused. Instead, he’s angry because he wants the country to make a certain kind of progress, and he’s increasingly angry to the extent that he feels the barriers to progress are unfair. It’s perceived injustice that animates Sanders, who’s as given to grumpy feistiness as Donald Trump is to jeering and pouting.

To really grasp what Sanders is about, you need to turn to behavioral economics — a Nobel prize-winning version of economics that factors in emotions when contemplating people’s decision-making behavior. One principle of behavioral economics is inequality aversion. Research has shown that people’s instinct for wanting fairness and justice is so strong that it can override all other considerations. People will harm their own self-interests, for example, and break off an otherwise profitable deal to avoid letting somebody else get the better of them in negotiations.

Feelings like outrage and vengeance are relevant then, while the motivations vary from altruism (“Let’s all play fair and be nice”) to injured self-esteem (“I’m no less important than you are!”).

The Sanders campaign isn’t an updated version of the Occupy Wall Street movement. It’s more like Occupy Main Street, Too. Emotions are contagious. Studies show that letting off steam doesn’t necessarily cause a person to calm down. In fact getting angry can make a person that much angrier, building the kind of emotional momentum that Sanders’s campaign events are feasting on. (And maybe Trump as well.)

Some pundits have compared Sanders to Senator Eugene McCarthy’s quixotic run for the Democratic presidential nomination in 1968. But emotionally that’s all wrong. McCarthy was aloof and wry. (When I asked him in 1988 about which of the seven deadly sins was the deadliest in politics, he answered, “Envy. In politics, sloth is a virtue.”) This is a far cry from the animated and cantankerous Sanders.

On Labor Day, Sanders used words like “grotesque” when talking about the current levels of income inequality and talked about the need for a “massive” redistribution of wealth. Sanders is going for the jugular.

Happiness might be deemed a luxury in the fight he’s waging against injustice. It might even be “off-emotion” in a campaign where Sanders looks ready to duke it out against the billionaires.

The more that Sanders gathers crowds and small donations, paradoxically the less happy he appears. Sanders told the Labor Day rally only once that “we’re going to win this election.” As the crowd erupted in cheers, then, and only then, did Sanders leave anger. He smiled.

But it wasn’t an actual smile. It looked more like a smirk. It seemed to reveal the senator’s contempt for all the usual “we’ll win” campaign claptrap. Even as he was using it.