according to a Pew Research Center poll conducted March 7-14, both white mainline and evangelical Protestants continue to approve of Trump as president at higher levels than other religious groups.

An article in the Washington Post argues:

The more someone believed the United States is — and should be — a Christian nation, the more likely they were to vote for Trump

First, Americans who agreed with the various measures of Christian nationalism were much more likely to vote for Trump, even after controlling for a host of other influences, such as political ideology, political party, and other cultural factors proposed as possible explanations of Trump voting.

How much a U.S. voter feared Muslims was as significant in predicting who voted for Trump as Christian nationalism. Overall the strongest predictors of Trump voting were the usual suspects of political identity and race, followed closely by Islamophobia and Christian nationalism.