“Nones,” as the religiously unaffiliated are called, make up 28% of Democrats and Democratic-leaning adults, Pew’s Religious Landscape Survey found, compared with 19% in 2007, the last time it studied the issue.

Christians overall still make up a majority of the Democratic Party, 63%. Catholics comprised 21% of the party as of 2014, down from 24% in 2007, the Pew study concluded.

Evangelicals remain by far the largest single religious group in the Republican Party, with a 38% share. But nones have grown in the GOP ranks, too, to 14% of the party in 2014, compared with 10% in 2007, the study found. Pew surveyed more than 35,000 adults by phone for the study.

The impact of the nones on politics “remains to be seen, since at least to this point, religious nones really punch below their weight, politically speaking,” said Greg Smith, the primary researcher on the Pew study. “They’re less engaged in the political process.”