Donald Trump, speaking aboard the World War II battleship USS Iowa, on Sept. 15, 2015, in San Pedro, Calif. (Robyn Beck/Agence France-Presse via Getty Images)

It’s impossible to identify all the reasons Donald Trump won the presidency. In a close election, virtually anything could have tipped the balance: small changes in turnout, Russian hacking, fake news, James B. Comey, mistaken campaign strategy, brilliant campaign strategy, a vulnerable opponent, email servers and so on.

A different, and perhaps more important, question is simply why a candidate such as Trump is appealing to so many Americans and yet deeply off-putting to so many others. In the long run, the sources of these deep and enduring political divisions is of greater consequence than any one election’s outcome.

A string of recent findings points to a key source of these divisions: people’s sensitivity to threat. Some people attend and respond more to potential dangers in the world and therefore are attracted to policies and candidates that they think will offer protection from threats.

Here are some of these findings:

  • My colleagues and I asked people to pick out angry as opposed to happy faces in a crowd.  People who were quicker to spot the angry faces were more likely to support “protective” policies that promote law and order, defense, gun rights, immigration restrictions and traditional lifestyles.
  • In another study, we used an eye tracker to determine how much people looked at positive images (cute bunnies and pretty sunsets) instead of negative ones (vicious dogs and wrecked cars) when given the choice. Those who “dwelled” on the negative images were also more likely to support “protective” policies.
  • We showed research participants 120 images — some negative and threatening; some positive and comforting — and, after a break, brought them back to see which images they remembered seeing. Those who disproportionately remembered the negative as opposed to the positive images were more likely to support protective policies.
  • We measured people’s basic physiological responses as they were looking at threatening, troubling images or responding to unexpected auditory startles. Those who registered the strongest biological responses again were the most supportive of a similar collection of protective policies.
  • We documented significant correlations between people’s political views and brain activation patterns as research participants looked at disturbing, threatening images.

In sum, people who are “threat sensitive” experience the world in a fundamentally different fashion than people who are not.

Threat-sensitive people then gravitate toward policies and candidates they think will protect them from threats, especially those threats posed by out-groups and in-group norm violators (the two most deadly dangers throughout human existence). People who are less threat-sensitive are mystified by the allure of these same policies and candidates. And so feelings intensify; battle lines harden; tribal conflicts clarify; political stalemate descends; the social fabric frays.

The relevance of this account to 2016 is not difficult to imagine. Whether by design or happenstance, Trump speaks the language of threat-sensitive individuals in a way that candidates such as Hillary Clinton, Barack Obama and Mitt Romney do not.

During the campaign Trump offered a dark view of the state of the nation, one in which threats lurk everywhere and a diminished United States is no longer able to confront them. A vote for Trump was a vote for someone who would take these threats seriously. Threat-sensitive individuals felt liberated and emboldened. Finally, someone got them. They then confronted their less threat-sensitive fellow citizens in a way the latter found deeply disconcerting.

Of course, previous elections have been fought over similar issues. (A relatively recent example is 1968.)  Although these elections tend to be unusually bitter, we have always recovered from them. On the other hand, the ability of those with a given level of threat sensitivity, whether high or low, to surround themselves with individuals and messages that affirm their predispositions has never been so great. More than in the past, this constant reinforcement creates a vicious downward spiral.

Can anything be done?  It won’t be easy. Perhaps the place to start is to change people’s perception of those who disagree with them. Individuals high in threat sensitivity see those on the other side as naive, clueless, and so insufficiently vested in the welfare of the in-group that they constitute a threat to the country. Meanwhile, individuals low in threat sensitivity see those on the other side as angry, fearful, and racist. Although perfidy and racism must never be tolerated, not all strongly held political positions cross those lines. And not all of them result from insufficient thought or from exposure to bogus information.

In other words, you can support certain immigration restrictions without being racist, just as you can kneel during the national anthem without being treacherous.

We must take more seriously the psychological and biological sources of political attitudes. As harmful as biased media outlets and fake news might be, the real problem is people’s eagerness to consume information that, however bizarre, pleasingly affirms their existing biases.

Those whose threat sensitivity is different from ours will continue to tailor their politics to the way they experience the world. We need to accept that, as baffling and maddening as we find them, they are not going away.

John R. Hibbing is the regents professor of political science at the University of Nebraska at Lincoln and co-author of “Predisposed: Liberals, Conservatives, and the Biology of Political Differences.”