Supporters of President-elect Donald Trump rejoiced across the nation on Election Night as their candidate defied the polls. (Monica Akhtar/The Washington Post)

Each week, In Theory takes on a big idea in the news and explores it from a range of perspectives. This week we’re talking about voter rationality. Need a primer? Catch up here.

Robert Kurzban is a professor of psychology at the University of Pennsylvania. Jason Weeden is a researcher and lawyer. Their recent book is “The Hidden Agenda of the Political Mind: How Self-Interest Shapes Our Opinions and Why We Won’t Admit It.

Hillary Clinton’s use of the word “deplorables” to refer to half of Trump’s supporters has taken a familiar tone when it comes to election contests. Partisans often view the other side’s voters as immoral, ignorant and irrational.

While research tells us that humans are subject to any number of biases, shortcomings and prejudices, support for Trump — or Clinton — need not, and probably should not, be attributed to these sources. Instead, the patterns of support for the two major candidates reveal a public that tends, on average, to match their votes to a range of rational, competing interests.

Some commentators, for example, wondered why white evangelical Christians supported Donald Trump despite his marital record and his remarks and alleged sexual assaults against women. Yet Trump nonetheless was clearly more likely than Clinton to advance the objectives typical of white evangelicals, including the appointment of pro-life federal judges.

These kinds of objectives are not merely symbolic, but reflect genuine, real-life conflicts. Our own research shows, for example, that supporters of abortion rights tend to engage in years of casual sex while simultaneously carefully controlling their timing of reproduction and amount of childbearing. Favoring access to abortion and birth control, and opposing efforts to stigmatize casual sex, is therefore a defense of rational interests for these people.

Their opponents, however, travel a more monogamous path with less-controlled fertility. And they often view those with more casual sexuality as disruptive to their lifestyles. (Think of it as trying to stick to a diet in an office where everyone else has candy bowls on their desks.) The efforts of religious conservatives to make casual sex more costly and difficult is also a defense of rational interests.

It is perhaps even easier to see competing interests at work with immigration and trade. While economists generally agree that immigration and trade are good economically, it is simultaneously the case that they aren’t good for everyone. Low-skilled immigrants and their families clearly benefit from accessing the U.S. labor market, but in doing so they create more job competition for low-skilled natives. Free trade lowers prices that consumers pay for many goods and boosts profits for the investor class, but also offshores some formerly good-paying jobs that less-educated natives might find difficult to replace.

Such observations help explain Trump’s appeal to whites without college degrees, but there is clearly more to it than that. Trump’s promise to “make America great again,” coupled with some of his best-known proposals — overturning “political correctness,” building a wall, banning Muslim immigrants, stop-and-frisk policing of minorities — involve perhaps the most central and tangible matters driving contemporary politics. These issues are about the basic competition between group-based discrimination and meritocracy.

In the not very distant past, social advantages were primarily given to white, heterosexual, native-born Christian men and only secondarily based on test-based and education-based meritocratic concerns. The last few decades have flipped these priorities. Trump’s core constituency involved not just low-education whites, but more specifically low-education, white, heterosexual, native-born, Christian men — in other words, just the sort of constituency that had relative benefits under the old rules but faced a material loss in privilege under the new meritocratic priorities. While those of us who are the winners from meritocracy might find such views deplorable, it would be difficult to maintain that their solid support for Trump was not in their tangible interests.

Similar arguments apply to supporters of “crooked Hillary.” How could they overlook emails, the Clinton Foundation, her pandering to Wall Street and her husband’s sexual history? Well, Clinton’s core supporters were the demographic reverse of Trump’s — minorities, immigrants, gays and lesbians, non-Christians and women, particularly those with more education. Her supporters also had much to gain from her policies and priorities.

The new core of the Republican party, Trump Republicans, don’t represent a particular puzzle. They plausibly showed up to the polls this year because they would be better off under the policies that Trump emphasized in his campaign. And, having flexed their muscles, they are likely to continue seeking expanded influence. Not because they’re irrational, but because they are self-interested — something generally true of voters on both sides.

Read more:

Jason Brennan: The problem with our government is democracy

David Greenberg: In defense of political spin