Republican presidential candidate Donald Trump remarked on Democratic presidential contender Hillary Clinton's brief absence from the debate stage on Dec. 19 saying, "Where did she go? I thought she quit." (Reuters)

On Monday night, Donald Trump made his latest polarizing comment, saying it was “too disgusting” to talk about Hillary Clinton’s use of the bathroom during the last Democratic debate and that she had got “schlonged” by Barack Obama when she lost to him in the 2008 Democratic primary.

Trump was surely talking off-the-cuff in his usual style — and the comments were criticized as offensive and sexist — but it was another example of his mastery in exploiting the psychological biases of conservatives who see much to dislike in today’s society and express support for Trump in the polls.

In fact, a growing mass of academic research has shown that conservatives have a particular revulsion to “disgusting” images. In this line of thinking, Trump’s decision to describe Clinton, one of the most disliked people by conservatives, as a “disgusting” figure would have been an especially powerful way to rile up his supporters.

The research — still debated — suggests that psychological and even biological traits divide people politically, both in the United States and abroad. These are attributes that may help explain why Trump has been so popular among a segment of the electorate, confounding political and media elites.

Republican presidential frontrunner Donald Trump has found a groove for his campaign rallies - poll numbers, protesters, Putin, and of course, making America great again. Here we break down the rally on Dec 21 into the required parts. (Gillian Brockell/The Washington Post)

Some of the recent research has been most pronounced evaluating the differing responses of conservatives and liberals to “disgusting” or “negative” images. Several studies have shown that conservatives are far more likely to have strong reactions to these images or situations than moderates or liberals are. Researchers have also suggested that conservatives are more likely to respond negatively to threats or be prone to believe conspiracies, perhaps helping explain why Trump’s calls to temporarily ban Muslims from entering the United States or build a wall at the southern border have resonated with many voters.

In a 2008 study in the journal “Cognition and Emotion,” researchers at Cornell and Yale asked 181 adults from across the political spectrum about their views on a range of matters. Participants were asked to rate their agreement to statements like “I try to avoid letting any part of my body touch the toilet seat in a public restroom, even when it appears clean” and to indicate how disgusting they found situations like “You take a sip of soda and then realize that you picked up the wrong can, which a stranger had been drinking out of.”

Across most metrics — including partisan affiliation — there were no noticeable differences among demographic groups in their response to these statements and questions.

But this wasn’t true of all groups. Conservatives showed a statistically significant likelihood of reacting negatively to “disgusting” situations. (So did religious groups, but the researchers determined the finding about conservatives remained true even when controlling for religiousity.)

Another, more recent study showed that the response to disgust may be hard-wired into our brains — even when we don’t consciously perceive it.

In a paper published in 2014 in Current Biology, researchers at the Human Neuroimaging Laboratory and the Computational Psychiatry Unit at Virginia Tech showed 83 subjects “disgusting” pictures of dead animal bodies, dirty toilets, as well as pleasant images such as pretty landscapes and babies playing together. The participants took a standard test to evaluate their political leanings.

Consciously, liberal, moderate and conservative participants showed no significant differences in rating these pictures, although conservatives “had marginally higher disgust sensitivity than the liberal group.” But things changed when the subject had their brains scanned using fMRI machines as they saw the images.

With a more than 90 percent success rate, the researchers were able to predict whether the participants were conservative or liberals based on how regions of their brains lit up while viewing the images. And it turned out that conservatives had a much stronger reaction to disgusting images than liberals. Reactions to other types of images were not predicted by political views.

“Disgusting images … generate neural responses that are highly predictive of political orientation,” the authors write. “Remarkably, brain responses to a single disgusting stimulus were sufficient to make accurate predictions about an individual subject’s political ideology.”


U.S. Republican presidential candidate Donald Trump reacts to supporters at the start of a Trump for President campaign rally in Raleigh, N.C., on Dec. 4. (Jonathan Drake/Reuters)

Others have suggested that disgusting images can even alter people’s political leanings.

A 2012 paper by Cornell University researchers tested the response of students to the presence of a hand sanitizer. The researchers asked random students a series of questions about their backgrounds and political leanings in a university building, and then asked them either to step over to the empty side of the hallway or to “step over to the hand-santizer dispenser to complete the questionnaire.”

The study found that “participants who reported their political attitudes in the presence of the hand-sanitizer dispenser reported a less liberal political orientation … than did participants in the control condition.” The researchers then ran a second, similar study and found the same response.

“It is worth noting that the cleanliness reminder used in these studies was quite subtle — in one case, through simple exposure to a public hand-sanitizer station and in another case via a sign on the laboratory wall reminding experimenters to wash their hands,” the researchers write. “It is notable that simply reminding participants of physical cleanliness rather than involving them in direct physical cleansing was sufficient for the effect to emerge.”