Looking at the evidence, we believe that both of these characterizations explain support for Donald Trump. In fact, we believe it to be unlikely that a candidate can win a primary emphasizing only one issue or addressing one particular personality type; Trump’s support stems from two groups with different psychological traits, who look for different things in a candidate.

When categorizing politicians like Trump, Paul Ryan and Bernie Sanders, it is of essential importance to make a distinction between politicians who express an anti-establishment message and politicians who express an anti-immigration message.

Sometimes these two messages go hand in hand. This is the case with Trump, who fiercely criticizes the Washington elite and at the same time aggressively insults immigrants. Yet these two messages need not be related.

Sanders, for instance, expresses an anti-establishment message that is not anti-immigrant, whereas Ryan holds restrictive ideas about immigration but is not anti-establishment (he was after all, the running mate of Mitt Romney during the 2012 presidential elections and is the current speaker of the House of Representatives).

Based on our earlier work (ungated here), we expect that voters who score low on agreeableness are likely to vote for an anti-establishment politician. This means that when it comes to this trait, supporters of Trump (who is anti-establishment) will differ from supporters of Ryan (who is not).

On the other hand, we expect that authoritarians are likely to vote for politicians who are restrictive on immigration. This means that in this respect Trump and Ryan supporters will not differ from each other. Both are, after all, restrictive toward immigrants.

Authoritarian citizens will differ, however, from those who support Hillary Clinton and Barack Obama and are generally pro-immigration.

Agreeableness, Authoritarianism and Support for Trump

To see if this is the case, we looked at the associations between agreeableness and authoritarianism on the one hand and support for Trump on the other hand. We report data that were collected between July 4 and 6 via Survey Sampling International in the United States among 882 Americans.

We measured the self-reported favorability of Trump, Ryan, Clinton and Obama on scales ranging from “very unfavorable” (1) to “very favorable” (5).

Figure 1 (left-hand panel) projects the predicted support for all four politicians, where a positive number indicates a positive association between the personality trait and support for the politician. In our models, we control for sex, age, education, income and race.

As expected, agreeableness is negatively associated with support for Trump but unrelated to support for Ryan, Obama and Clinton. We also find in the bottom panel of Figure 1 that authoritarianism is positively associated with support for both Trump and Ryan but negatively associated with support for Obama (and unrelated to support for Clinton).

This evidence confirms that agreeableness but not authoritarianism distinguishes support for Trump from support for other Republicans who are restrictive on the issue of immigration.

Figure 1 – Agreeableness and authoritarianism as correlates of support for Trump, Ryan, Clinton and Obama (Bert Bakker)

Anti-establishment and anti-immigration messages

In the same survey, we conducted an experiment to further assess whether agreeableness and authoritarianism affect support for (fictional) politicians expressing an anti-establishment or anti-immigration message.

Participants were asked to make a decision in a fictional election for the House of Representatives for candidate A or B. Candidates could express an anti-establishment message (“The House of Representatives is mostly full of Washington insiders who only care about themselves”) or a pro-establishment message (“The House of Representatives is mostly full of honest and hardworking people who care for ordinary Americans”).

We also varied the stances of the fictional candidates toward immigration. On the one hand, a candidate could be pro-immigration with claims like “immigrants from countries that are torn apart by war or natural disaster should be welcomed in America” or“immigration is good for our economy; immigrants can take up vacant jobs and bolster economic growth.”

On the other hand, the candidate could be anti-immigration, making statements like“immigrants steal jobs from ordinary Americans; we should stop immigration!” and“America is for Americans, therefore we should stop immigration!”

Figure 2 shows that individuals are more likely to vote for a candidate who makes an anti-establishment claim only when they score low on agreeableness. The horizontal axis represents the level of agreeableness, and the vertical axis shows the effect of expressing an anti-establishment message on supporting that candidate.

The histogram shows the distribution of agreeableness. A positive effect indicates that the anti-establishment message leads to more support for a politician. The diagonal solid line indicates that the effect of the anti-establishment message on candidate support decreases if the level of agreeableness increases. The gray area around the line represents the 95 percent confidence interval.

Thus, the graph clearly shows that there is a positive and statistically significant effect only for low levels of agreeableness. Such an effect does not exist vis-à-vis authoritarianism.

Figure 2 – Effectiveness of the anti-establishment message over the range of agreeableness (Bert Bakker)

We do find an association, however, between authoritarianism and the likelihood of voting for a candidate who expresses an anti-immigration message.

Figure 3 projects the effect of the message that immigrants steal jobs from Americans over the range of authoritarianism. The graph shows that a candidate who expresses such a message receives more votes than a candidate expressing the message that the U.S. should take care of refugees, but only among strongly authoritarian citizens.

Figure 3 – Effect of the anti-immigration message over the range of authoritarianism (Bert Bakker)

To summarize, the personality trait agreeableness is one that unifies citizens who vote for anti-establishment parties and politicians. The reason is, most likely, that the anti-establishment message resonates well among low-agreeable citizens.

Authoritarianism distinguishes individuals who support candidates who express anti-immigration messages from supporters of pro-immigration politicians. Because Trump is both fiercely anti-establishment and ferociously anti-immigrant, he receives a lot of support from both groups.

After all, the anti-establishment message only resonates with the personality of some voters.

Bert Bakker is an assistant professor of political communication at the University of Amsterdam. Matthijs Rooduijn is an assistant professor of sociology at Utrecht University. Gijs Schumacher is an assistant professor of political science at the University of Amsterdam.

This article presents the views of the authors and not the position of USAPP – American Politics and Policy nor the London School of Economics.