American politicians who openly express religious views may be more successful because even voters who think that religion should not play a role in politics view them as more trustworthy compared with non-religious candidates, according to a study published in American Political Research.

The central role of religion in American politics has long been a point of debate. Surveys of the American public show that only 30% would be willing to vote for an atheist candidate. Although religious people are most strongly associated as a constituency of the Republican party, previous research has shown that Democratic candidates also emphasize their own religiousness frequently, and are more successful when they do so.

A study led by Scott Clifford, of the University of Houston, examined multiple sources of data on Americans’ religious and political attitudes to understand why talking about religion seems to benefit members of both parties when it comes to winning votes.

First, using data a 2007 Newsweek poll of 1,004 Americans, the researchers found that the most important factor influencing a person’s willingness to vote for an atheist was whether or not they believed that atheists were capable of being moral. Nearly 30% of those polled said that atheists could not be moral people, and those who felt this way were less likely to say they would consider voting for an atheist by 68 percentage points.

Next, using data from a 2007 CBS News poll of 1,282 Americans, they looked at the impact of perceptions about religion and trustworthiness for a specific politician: Hillary Clinton, then a candidate in the Democratic presidential primaries. Among liberals, perceptions about Clinton’s religiousness had no impact on their ratings of how honest they felt she was. But among moderates and conservatives, the more voters felt that Clinton was a strongly religious person, the more highly they rated her honesty. For all voters, liberals as well as moderates and conservatives, the stronger her religious convictions were perceived to be, the more likely people were to give her favorable ratings overall, and the more likely they were to say they would consider voting for her.

Finally, the study team conducted a new experiment with 311 Americans recruited on the internet. People read a short description of a politician and were asked to rate him on morality. Half of the participants were told that the politician was a Republican and the other half were told that he was a Democrat. Within each of these groups, for one third of participants the candidate was described as strongly religious, one third as a strong atheist, while the final third received no description of the candidate’s religious orientation.

Religious voters felt that the religious candidate was more moral, whereas non-religious voters rated the atheist candidate more highly on morality. Importantly, however, the atheist candidate was much more polarizing. Non-religious voters remained relatively favorable towards the religious candidate, but religious voters viewed the atheist candidate very negatively.

Put together, these findings suggest that even Democrats have much more to gain among moderate and conservative voters by emphasizing their religious values than they have to lose among liberals. But the authors of the study also note that as the number of atheists and other non-religious voters continues to rise, particularly in younger generations, the political advantages of being religious may begin to decline.