"Christians account for the majority of registered voters in the U.S. (64%). But this figure is down from 79% as recently as 2008."
https://www.pewresearch.org/fact-tank/2020/10/26/what-the-2020-electorate-looks-like-by-party-race-and-ethnicity-age-education-and-religion/
"A report by Pew published in its U.S. Politics & Policy section found that while 73% of Democrat voters were Christian in 2008, by 2019 the percentage had dropped to 52%."
https://www.christianpost.com/news/democrat-voters-who-identify-as-christian-has-plummeted-since-2008-pew.html
Christians by political party
https://www.pewresearch.org/religion/religious-landscape-study/compare/christians/by/party-affiliation/
"The Pew report also analyzed the religious affiliations of members of the 117th Congress by party. Some 98.9% of the Republicans in Congress identify as Christians compared to 77.8% of Democrats."
https://www.christianpost.com/news/religious-makeup-of-the-117th-congress-is-88-christian.html