WASHINGTON — The overwhelming majority of federal lawmakers in the U.S. are Christian, according to a new report, which also found that Catholics in the legislative branch are split between parties, reflecting a split in the U.S. population.

More than 90% of the 114th Congress identifies as Christian: about 20% higher than the average among adult Americans, said the Pew Research Religion and Public Life Project.

“Protestants and Catholics continue to make up a greater percentage of the members of Congress than of all U.S. adults,” the report stated, adding that, “despite the sea change in party control,” those numbers had not shifted significantly from the previous Congress.

Two-thirds of Republicans are Protestant, and about a quarter are Catholic, according to the report. In contrast, 44% of Democrats identify as Protestant, and 35% say they are Catholic. In the U.S. Senate, where Republicans picked up nine seats this past election cycle, still more Democrats are Catholic than Republicans.

Of the rest of the members, most are either Jewish or Mormon, with only one member “unaffiliated” with any religion.

The fact that almost every member of Congress identifies with a religion reflects a long-standing political trend, said Matthew Green, a professor of politics at The Catholic University of America in Washington.

“It has long been politically risky for elected officials at the national level to be unaffiliated with a particular religion or church,” he told CNA, noting that candidates “who are spiritual or religious risk being seen as suspect in an election campaign if they do not identify with a specific religious faith or church.”

Although the House is overwhelmingly Republican and the Senate is majority Republican, the number of Catholics in both parties is split almost evenly in the House and is majority-Democrat in the Senate. Catholics have become a critical swing vote in election cycles, Green said, and the numbers in Congress reflect this.

“If the number of Catholics in the House is now close to 50-50, that's an important development and a very strong sign of the extent to which the Catholic vote has become the ‘swing’ vote in American politics; and politically ambitious Catholics can find avenues for success in either party,” he told CNA.

The fact that more members of Congress identify as Christian than the American populace might be explained by demographics, he added.

“There may be political reasons that some incumbents identify as Christian,” Green acknowledged, but he added that the rise of “unaffiliated” Americans is a recent phenomenon.

“I would not be surprised if the disproportionate number of the religiously unaffiliated are younger Americans, as opposed to the mostly older people who run for, and get elected to, the House and Senate,” he said.

However, “for many years, atheism has been called the ‘last taboo’ in American politics,” he noted, pointing to another Pew Research study from May showing atheism as the top negative quality that voters see in a potential 2016 presidential candidate.

Fifty-three percent of respondents said they would be “less likely” to vote for an atheist candidate, compared to 41% who said it “wouldn’t matter,” and 5% who said they would be “more likely” to vote for the candidate. For comparison, 35% of respondents said they would be “less likely” to vote for a candidate who had an extramarital affair.