Donald Trump delivers the convocation at Liberty University, which was founded by evangelist Jerry Falwell, on Jan. 18, 2016, in Lynchburg, Va. (Chip Somodevilla/Getty Images)

For at least three decades, the Republican Party has won the votes of self-identified evangelicals. According to 2004 exit polls, George W. Bush won 78 percent of their votes; in 2008, John McCain won 74 percent; and in 2012, Mitt Romney won 78 percent.

So it’s no surprise that Donald Trump has made overtures to the evangelical community. More surprising, perhaps, is that evangelicals are reaching back. A thrice-married, admitted adulterer who has publicly boasted about his sexual prowess seems hardly a model candidate for right-wing religious voters.

But our new research suggests that evangelical voters’ views of Trump probably have much less to do with him personally than with his rhetoric on abortion and his promises to protect Christianity in America.

That’s because of the emotional power evoked by moral judgments about human sexuality and family structure. Those subjects evoke stronger feelings than most other political or personal issues. People adjust their party loyalties, we find, to fit their views on “culture war” issues. Seen that way, Trump’s personal religious convictions or behavior appear far less important than his pro-life stance on abortion and promise to fight for a particular version of religious liberty, which many evangelical Christians and orthodox Catholics see as signaling resistance to same-sex marriage.

Republican presidential candidate Donald Trump told conservative pastors in Florida, Aug. 11, that if he's elected, they will "have great power." Trump pledged to take on a law that bars tax-exempt organizations from getting involved in political campaigns. (The Washington Post)

Voters don’t easily change their opinions on culture-war issues

Our argument and findings break with standard political science views. Classic and contemporary research argues that partisanship is more stable over time than are issue attitudes, and that party identification influences people’s issue positions most of the time. There are exceptions, of course (see here, here and here). But most of the discipline has believed that party drives issue positions, not the other way around.

In our research, we looked at Americans’ attitudes toward abortion and LGBT rights. We used public opinion data that involved interviews with the same individuals at two different points in time. Such polls, known as “panel” surveys, are especially valuable because they allow us to examine over time people’s partisanship and their positions on moral issues. We can also gauge whether one is more likely to influence the other.

Our four panel data sets come from the National Election Studies, the General Social Survey, and the Portraits of American Life Study. They cover periods from 1992 to 1996, 2006 to 2010, 2008 to 2012, and 2006 to 2012.

We first tested the standard conventional wisdom: that party identification is more stable over time than people’s attitudes on abortion and gay rights. We found that it was not.

The average over-time correlation — a measure of the consistency of voters’ opinions — was 0.78 for party identification. For the two culture-war issues, the correlation was 0.77. The party identification and culture-war correlations we report are very stable according to the standards used to judge over-time correlations. In other words, voters’ opinions about culture-war issues are as strong as their partisan attachments.

Speaking in Cleveland on the third day of the Republican National Convention, Liberty University President Jerry Falwell Jr. talks about why he's supporting Donald Trump, a presidential candidate who doesn't always line up with Evangelicals on social issues. (Dalton Bennett/The Washington Post)

Are Americans changing party to fit with their culture-war beliefs?

That led us to our next question: Are Americans adjusting the party they identify with — and perhaps the candidates they vote for — based on their positions on these hot-button issues?

To answer this question, we wondered whether people’s abortion and gay rights attitudes measured in an initial survey — say, 2006 — would predict their party identification in a later survey — say, 2012. If culture-war attitudes are an especially strong influence on voters’ loyalties, we should find that their positions on those issues should lead them to identify more closely with the party that matches their positions — taking into account how strongly they identified with their party to begin with.

They did, in fact, update their party loyalties based on culture-war issues, as we found in all four of our panel studies. Averaging across our data sets, the most culturally conservative people (i.e., antiabortion and anti-gay rights respondents) move nearly 16 percent more toward the Republican Party over time than do the most culturally liberal respondents. That suggests that people are choosing their party based at least in part on how they feel about these controversial moral issues.

Not surprisingly, we also found evidence for the conventional view: that people’s partisanship influenced their positions on issues. But partisanship had a weaker effect on issues than issues had on partisanship.

For instance, people who identified themselves as “strong” Republicans in an initial survey became 5 percent more conservative on abortion and gay rights over time, compared with “strong” Democrats. This is only about one-third of the reverse: how much individuals’ feelings about the issues shifted their identification with a party.

In fact, those culture-war issues influenced individuals’ positions on more than just their political party. Over time, we found that people’s positions on abortion and gay rights led them to change their religious practices. For instance, individuals with liberal views on abortion and same-sex marriage became less likely to say they had a daily commitment to religious practices.

Republican presidential nominee Donald Trump has vowed to repeal the 'Johnson Amendment' because he says it infringes on the freedom of speech of religious groups. Here is what you need to know about this amendment. (Bastien Inzaurralde/The Washington Post)

This isn’t a complete break from all past research. Other scholars have found that people sometimes change their religious identities to line up with their party identifications  and political ideologies. Profound moral beliefs are sometimes known to lead people to change their religious affiliations.

But our findings do contrast with those of many scholars. The political scientist Gabriel Lenz, for instance, has found that people often switch their positions on issues to line up with those of a candidate they support. We don’t find that that happens on abortion and LGBT rights. Feelings about moral issues may well be uniquely — or at least especially — powerful.

To be sure, our study does not prove that culture-war issues cause people to change parties, religions, or opinions about presidential candidates. We simply find that these questions do exert a stronger pull than many others.

As a result, Trump will probably maintain his advantage among evangelicals as long as he espouses their conservative positions on moral issues. Put simply, moral issues matter as much as party, and perhaps more than personal character.

the science of trump

Paul Goren is a professor of political science at the University of Minnesota and the author of On Voter Competence.

Christopher Chapp is an assistant professor of political science at St. Olaf College and the author of Religious Rhetoric and American Politics: The Endurance of Civil Religion in Electoral Campaigns.