You can see this process at work in research published last year by the psychologists Anneke Buffone and Michael Poulin. Subjects were told about a competition between two students in another room of the lab. Half of the subjects read an essay in which one of the students described herself as being in distress (“I’ve never been this low on funds and it really scares me”); the others read an essay in which she was mellow (“I’ve never been this low on funds, but it doesn’t really bother me”). The subjects were then told that they were going to help out in a study of pain and performance, wherein they would get to choose how much hot sauce the student’s competitor would have to consume.

Keep in mind that this competitor didn’t do anything wrong; he or she had nothing to do with the student’s anxiety about money. Nonetheless, the subjects chose to give more hot sauce to this other person when the student was described as distressed. Their empathy drove aggression, even when it made no moral sense.

Also, before the study was done, Buffone and Poulin gave all of their subjects a test that scans for specific genes that make people more sensitive to vasopressin and oxytocin, hormones that are implicated in compassion, helping, and empathy. As predicted, there was a greater connection between empathy and aggression in those subjects that had those genes—that is, more empathic people were more aggressive when exposed to the suffering of strangers.

I’ve come up with similar findings in a series of studies done in collaboration with the Yale graduate student Nick Stagnaro. We start by giving people a simple test that measures their degree of empathy. Then we tell them some awful stories, about journalists kidnapped in the Middle East, about child abuse in the United States. And then we ask them how best to respond to those responsible for the suffering. In the Middle East case, we give a continuum of political options, from doing nothing to public criticism, all the way to a military ground invasion. For the domestic version, we ask about increased penalties for the abuser, from increasing their bail to making them eligible for the death penalty. Just as with the genetic study, we found that the more empathic people are, the more they want a harsher punishment.

Politicians are comfortable exploiting this dark side of empathy. Donald Trump likes to talk about Kate—he doesn’t use her full name, Kate Steinle, just Kate. She was murdered in San Francisco by an undocumented immigrant, and Trump wants to make her real to his audience, to make vivid his talk of Mexican killers. Similarly, Ann Coulter’s recent book, Adios, America, is rich with detailed descriptions of immigrant crimes, particularly rape and child rape, with chapter titles like “Why Do Hispanic Valedictorians Make the News, But Child Rapists Don’t?” and headings like “Lost a friend to drugs? Thank a Mexican.” Trump and Coulter use these stories to stoke our feelings for innocent victims, to motivate support for policies against the immigrants who are said to prey upon these innocents.