Party and Religion

From Pew:

The U.S. religious landscape has undergone profound changes in recent years, with the share of Christians in the population continuing to decline.

These shifts are reflected in the composition of the partisan coalitions. Today, Christians make up about half of Democratic voters (52%); in 2008, about three-quarters of Democrats (73%) were Christians. The share of Democratic voters who are religiously unaffiliated has approximately doubled over this period (from 18% to 38%).

The changes among Republicans have been far more modest: Christians constitute 79% of Republican voters, down from 87% in 2008. (Data on religious affiliation dates to 2008; prior to that, Pew Research Center asked a different question about religious affiliation that is not directly comparable to its current measure.)