This chart is from the Pew Religion and Public Life Survey done in August of 2022. It shows that all three major christian sects (evangelicals, mainline protestants, and catholics) have dropped significantly in the last 10 years. All three are now much smaller than the group of religious nones (those not professing any religious affiliation).
This could explain why the Republicans are trying so hard to force their evangelical brand of christianity on all Americans. They see a nation that was once very christian now becoming less christian with each passing year. And their evangelical base doesn't like it. If they can't remain on top by proselytizing, then they will do it through force of law.
It's the basis for christian nationalism - the belief that christianity should be the official national religion, and the basis for the nation's laws and regulations. It authoritarian, and goes against the secular values the nation was founded own.