It’s easy to find anecdotal evidence that America has grown more reactive, coarser, and less tolerant of outsiders since the 2016 presidential election.

Last week, congressional candidate Greg Gianforte body-slammed a reporter in response to a question about health care. Then he won a special election. Everyday Trumpisms like “Sad!” and “Loser!” seep deeper into conversations. Politicians become more brazen and crass in their dismissal of facts that don’t suit their worldview. And then there are hate-fueled crimes against Muslims and other minorities, like Friday’s deadly attack on a Portland train.

Empirically, though, a shift is much harder to pin down. But some preliminary evidence is starting to emerge that suggests America is becoming a more hostile place for outsiders.

“I don’t think Trump created new prejudices in people ... what he did do is change people’s perceptions about what is okay and what is not okay”

The most recent: A working paper in NBER wondered if Trump’s election acted as a validation of anti-immigrant sentiment. That if you could become president while stoking xenophobia — building walls, restricting immigration, trumpeting “America first,” etc. — would that make xenophobia more socially acceptable?

And it turns out the answer is yes: More participants in the study became willing to openly donate money to an anti-immigrant organization after the election. (Before the election, too, more participants were more willing to openly donate if they were told Trump’s victory was assured in their state.)

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“If Trump had not come on the scene, a lot of Americans would refuse to authorize a donation to an anti-immigrant organization unless they were promised anonymity,” writes Cass Sunstein in a column in Bloomberg. “But with Trump as president, people feel liberated.”

It’s only a preliminary bit of evidence, and behavior in an online experiment (as the authors of the NBER paper did) can’t easily be generalized to the real world.

But it squares nicely with decades of psychological research, which finds that we feel freer to behave badly when we witness bad behavior.

Kids become more aggressive when they see aggressive adults. Adults do the same.

In the 1960s, Stanford psychologist Albert Bandura showed how easy it is to teach kids to act violently — by showing them an adult acting violently.

In this famous experiment, Bandura showed young children — between 3 and 6 years old — a video of an adult wailing on an inflatable “bobo doll” (see in the video below). Other children in the study did not see an adult behaving aggressively to the doll.

And sure enough, the kids who saw the aggressive behavior were more aggressive themselves when playing with the doll later on.

It’s a simple experiment with a simple conclusion: As humans, even at an early age, we learn what’s socially acceptable by watching other people.

After the election, we witnessed an unsettling number of brazen hate crimes and vandalism against Muslim and Jewish institutions. Again: It’s hard to directly link these crimes to the charged political climate. But as with Bandura’s experiment, there’s evidence that social norms against prejudice change when people in power start talking and behaving badly.

Does Trump’s bad behavior trickle down?

Some psychologists think Trump’s rhetoric and the rise of the alt-right movement that supported him are similarly encouraging people who already have prejudicial views to act upon those views.

“I don’t think Trump created new prejudices in people — not that quickly and not that broadly. What he did do is change people’s perceptions about what is okay and what is not okay,” University of Kansas psychologist Chris Crandall told me in March.

That’s essentially what the authors of the NBER paper found.

That paper tested participants before and after the election. Before the election, 34 percent of participants said they’d donate to the anti-immigrant organization when those donations were to be made public. About 54 percent said were willing to donate if the donations were kept private. The difference between the two shows there was a social stigma attached to donating to the group. After the election, that stigma lessened: 48 percent of people said they’d donate in the public conditions. (The experiment was more complicated than that. Read a more in-depth take here.)

Crandall has also found preliminary evidence that this is the case.

Last year, Crandall and his student Mark White asked 400 Trump and Clinton supporters to rate how normal it is to disparage members people of various marginalized groups — like the obese, Muslims, Mexican immigrants, and the disabled — both before the election and in the days after.

Both Clinton and Trump supporters were more likely to report that it was acceptable to discriminate against these groups after the election. For Trump to say the disparaging things he said during the campaign, and then be rewarded for them, sent a powerful sign.

“It took away the suppression from the very highly prejudiced people,” Crandall said. “And those are people acting.”

Small transgressions turn into larger ones

Crandall’s results are preliminary (i.e., not yet published in a journal), but they’re reflective of the established literature: Exposure to misbehavior simply makes it more acceptable.

Here’s one example. In 2004, sociologists Thomas Ford and Mark Ferguson found that exposure to a racist or sexist joke increased tolerance of further discrimination in people who held prejudicial views. Hearing the off-color joke, they write, “expands the bounds of appropriate conduct, creating a norm of tolerance of discrimination.”

From there, small transgressions can lead to a slippery slope of larger ones.

A 2015 paper in the Journal of Applied Psychology had participants play many rounds of a Sudoku-like game. Correct answers in each round yielded a higher and higher cash reward, and the design of the study allowed for participants to lie about their scores.

In one arm of this experiment, the cash rewards increased very gradually, around 75 cents per round. In another arm, the cash reward jumped abruptly and dramatically to $2.50. Participants were more likely to lie about their scores in the gradual change arm. This shows we gradually habituate ourselves to lying, and become comfortable with it by little steps, not huge ones. “Exposure to slippery-slope conditions more than doubled the rates of unethical behavior in our studies,” the authors concluded.

There’s even some small evidence that societal corruption trickles down into everyday behavior. In 2015, researchers in the UK found across 23 countries that people are more likely to lie when they live in societies where corruption is rampant. “If politicians set bad examples by using fraudulent tactics like rigging elections, nepotism and embezzlement, then the honesty of citizens might suffer, because corruption is fostered in wider parts of society,” the study authors wrote in Nature.

In all, this research is a reminder: We need to keep our leaders accountable for their bad behavior. If we don’t, it may become the norm not just in politics but throughout American life.