WASHINGTON — Don’t expect any official “Atheists for Hillary” outreach, but political progressives are cheered by a study showing a rise in the number of nonreligious Americans.

It’s not because top Democrats are irreligious; President Obama and Hillary Rodham Clinton are persons of faith. But liberals welcomed the findings, in the 2014 Religious Landscape Study, which was released last week by the Pew Research Center and showed a country growing less religious. Republicans consistently do well among voters with strong religious beliefs, and Democrats score better with voters who don’t express religious views.

The study, a 35,000-person sample, reveals that over the past seven years, there has been a 10 percent decline in self-identified Christians, though they still are more than 70 percent of the population. At the same time, the religiously nonaffiliated, or “nones,” have increased by about one-third and now account for about 23 percent of American adults. This trend could have political implications. In the last presidential election, Mitt Romney easily won among Christian voters, and Mr. Obama carried 70 percent of the unaffiliated. This divide was even more apparent in the 2014 congressional elections.

Evangelical Protestants, the core of the Republican base since Ronald Reagan, have held steady over the past seven years, according to the study, though their share of the population has declined somewhat. In the last presidential and midterm elections, , in 2012 and 2014, evangelicals made up more than a quarter of the electorate and voted Republican by a four-to-one ratio.