President Trump’s language is plain and clear when he speaks of immigrants. They’re criminals, rapists, drug dealers, murderers. Foreign governments have sent them to us from their prisons and mental institutions. They’re poisonous snakes, robbing Americans of public benefits and jobs.

He’s made these claims hundreds of times, according to the Marshall Project, at themarshallproject.org. Their fact-checks indicate that all are misleading at best and more often simply false. Crime rates for immigrants, legal and otherwise, are, for example, far lower than for native-born Americans.

But statistics sometimes lose when they’re up against human nature. Distrust and fear of strangers is strong among us Homo sapiens, as well as many other animals. We can trace it in part to the prehistoric past, as cognitive scientist Mark Schaller explained in the Dec. 12, 2011 issue of the British journal, Royal Society.

We have since the earliest times felt disgust toward feces, rotten food, and anything else that could expose us to dangerous viruses and other germs, and have instinctively avoided them. Likewise for strangers from outside the community. They could carry new diseases to which local people had no immunity, and they might not follow local customs for cleanliness and disease-prevention.

People who are vulnerable to disease, or at least think they are, are likely to be especially fearful of outsiders. It happens to pregnant women during their first three months, when their immune systems weaken to avoid mistakenly attacking the fetus. Surveys reveal heightened feelings of xenophobia, which dictionaries define as “the fear or hatred of strangers or foreigners or of anything foreign or strange,” during this time.

The behavioral immune system, as scientists call it, errs on the side of caution. It reacts against people who don’t really present health hazards as well as those who do, crossing over from reasonable carefulness to bigotry and xenophobia. President Trump capitalizes on this when he talks about immigrants.

He appeals to our sense of disgust for rotten meat, feces, and other pollutants when he says that immigrants are poisoning the nation’s blood, have bad genes, and eat dogs and cats. He pulls on the same feelings when he compares them to Hannibal Lector and his fondness for human meat. Calling them animals, criminals, and mentally ill magnifies our sense of how different, and therefore how dangerous, they are.

The President and his allies multiply the persuasive power of these claims by relentlessly repeating them. Scientists call it the Illusory truth effect. Aumyo Hassan and Sarah J. Barber at cognitiveresearchjournal.springeropen.com on May 13, 2021, reported on their research, and that of others, revealing that the more often people hear a statement, the more likely they are to believe it, whether it’s true or not.

We can, once we’ve become convinced that immigrants are enemies who are less than fully human, justify treating them in ways we would otherwise oppose as un-American. Denial of due process, racial profiling, and inhumane detention conditions can now seem necessary, even desirable.

Mr. Schaller doesn’t claim that our instinctive fear of disease is the only influence on our attitudes toward immigrants. Our customs, beliefs and experiences also play a critical part. They can intensify our natural wariness toward outsiders or, instead, encourage an equally natural curiosity and attraction to them.

A balanced view avoids going to an extreme in either direction. It realizes the benefits as well as the risks of immigration. The President’s language represents, instead, a deep hostility toward immigration and immigrants, as seen in his reaction to the recent attack on two national guard members in Washington D.C.

Mr. Schaller cites evidence that the behavioral immune system no longer serves as an effective defense against disease. The President has nevertheless found it to be a persuasive political strategy with many Americans – but not all. A Pew Research survey, at pewresearch.org on June 17, 2025, reveals that majorities oppose many components of his immigration policy, such as workplace raids and suspension of most applications for asylum.

Most Americans aren’t persuaded by the President’s talk of pollution, disease, and disgust. They realize that immigrants are an important part of a healthy economy and society. This presents Democrats with an opportunity to claim the middle ground by offering a moderate alternative to the President’s anti-immigrant policies, one that balances the benefits of immigration with effective controls.

Lowell Harp is a retired school psychologist who served school districts in Ogle County. For previous columns, follow him on Facebook.