Former vice president Joe Biden, leading in the Democratic presidential nomination contest, has cast his campaign against President Trump as a battle for "the soul of our nation." In doing so, Biden suggested that the president's rhetoric has fanned the flames of prejudice and emboldened hate groups at home.

Biden is certainly not alone in his assessment. Since Trump's election, observers have argued that his racially inflammatory speech has emboldened people with deeply held prejudices to act on them — a phenomenon that the Southern Poverty Law Center, among others, refers to as the "Trump effect."

Is it true? Have Trump's remarks normalized public expressions of bias? In brief, yes. Our new study finds causal evidence suggesting that Trump's inflammatory campaign remarks have encouraged some Americans to voice prejudice toward Latinos.

What we aimed to test

We tested three hypotheses. First, we hypothesized that individuals who harbor prejudice and hear or read racially inflammatory comments by politicians are more likely to believe it is acceptable to express those views openly. We called this an "emboldening effect."

Second, we hypothesized that when other politicians besides Trump condone explicit racial rhetoric, that would amplify the emboldening effect; and when they condemn it, they would offset the effect, at least slightly.

Third, other politicians' condemnations would decrease the effect only among people who pay close attention to social norms, a group that social scientists refer to as "self-monitors."

Research approach

To test our hypotheses, we fielded a national survey of 997 respondents using Amazon's Mechanical Turk in two online waves in spring 2016, during the presidential nomination season.

In the first round, we asked respondents for their demographic information and political orientations. To measure their existing prejudice, we asked them to rate how well the words "intelligent," "lazy," "violent" and "here illegally" describe "most Hispanics" in the United States. We then combined the individual measures into a scale, which forms our underlying measure of prejudice.

During the second round, about a week later, each respondent read one of five randomly assigned articles drawing on what candidates had actually said. Each of the readings included an article on the primaries, focusing on two candidates — Hillary Clinton and one of the Republican candidates — and their positions on a political issue.

Here's what varied between the five readings: 1, whether the Republican candidate was Jeb Bush or Donald Trump; 2, whether the issue discussed was campaign finance reform or immigration; 3, whether Trump's racially inflammatory statements were included; and 4, among those who read Trump's racially inflammatory statements, whether other prominent political figures across both sides of the political aisle commented on Trump's statements. The last group was then divided into two. Half were told that leaders in both parties condemned Trump's statements, while the other half were told that party leaders have remained silent about Trump's statements.

Each respondent then read this short vignette:

Darren Smith is a middle manager at an accounting firm and has been working at the firm for nearly eight years. One part of Darren's job is to supervise the new interns for the accounting firm. While Darren usually likes the interns, he does not like a new intern named Miguel. Darren regularly throws away Miguel's leftover food in the break room fridge, claiming that “Miguel's food is greasy and smells up the fridge.”

We then asked respondents to rate Darren's social acceptability on a 5-point scale that ran from 1 (completely unacceptable) to 5 (completely acceptable) — a way to see what they thought of someone's publicly expressed bias.

Rhetoric brings out prejudice

We found that among those who had scored as "prejudiced" in our earlier assessment, reading Trump's racially inflammatory speech did make them feel more comfortable expressing it by approving of "Darren's" prejudiced behavior.

When respondents didn't read Trump's racially charged rhetoric, the opposite was true: Prejudiced individuals suppressed their prejudice by ranking "Darren's" prejudiced behavior as unacceptable. However, this "suppression effect" slowly unravels and gives way to tolerance and acceptance of prejudiced behavior following exposure to racially inflammatory speech by Trump. And the willingness to express racial bias got even stronger when the respondent also read about other political figures tacitly condoning his remarks.

But there wasn't much of a protective effect when the rhetoric was condemned. When respondents read about party leaders speaking out against Trump's remarks, it held back only those who scored high on self-monitoring, or roughly 40% of our sample.

The takeaways

When prominent political figures like Trump make racially charged statements, it can indeed let ordinary Americans feel that they can freely express their own bias. More important, that's especially true when other political figures don't speak up against those statements, which sends the message that those attitudes are acceptable.

We found something similar when we asked respondents to evaluate the survey administrator, whom we gave a common Latinx name, "Juan Ramirez." We told respondents that we were evaluating "Juan's" job performance, leading them to believe they could affect "Juan's" job. Exposure to Trump's racial rhetoric caused those high in prejudice toward Latinos to give "Juan" a very negative performance evaluation; personally behaving in a way that could subtly harm a Latinx person.

Finally, observers often argue that social changes like increased immigration or more racial diversity in an area are what activates otherwise suppressed biases. That's not entirely true; prominent political figures also have an influence. Racially inflammatory rhetoric tends to invite and encourage others to let their biases be known. That gets even stronger when such rhetoric goes unchallenged by other prominent political figures. But that spread isn't inevitable. When public figures speak out against racially charged comments, it does help prevent that sense of permission from spreading.

Benjamin Newman is an associate professor of political science and public policy at the University of California at Riverside. Also contributing to this commentary, all from UC at Riverside, were Jennifer Merolla, professor of political science; Sono Shah, a PhD candidate; Loren Collingwood, an associate professor of political science; and Karthick Ramakrishnan, a professor of political science and public policy.