The number of traditionalist Christians, defined by evangelical polling outfit Barna as those who attend monthly and say faith is important to them, has declined by almost half since 2000 
It took at 10-point drop in 2012 and has never recovered. Things have not reversed during the Trump presidency either. Although perhaps the floor may be reached since the decline has slowed.
According to Barna Group, half of formerly practicing Christians just became non-practicing while the other half became non-Christians
David Kinnaman, Barna president: "This shift has major repercussions for church leaders as there is increased struggle to attract and retain the active segment of churchgoers."
Church attendance generally is also down significantly. As late as 2009, 48% of U.S. adults claimed to sit in a pew weekly. Now, only 29% say this
The decline in attendance exists across generations.
The percentage of people who say they pray weekly has not declined by as much, however. In 2009, it was 85%, in 2020, it's 69%
Even as the raw number of traditionalist Christians has declined, however, their vote share has not. In fact, people who are in this group are much more likely to vote than those who are more secular
In essence, as the influence of traditionalist dogma on society declines (see evolution, LGBT, science generally), traditionalist Christians are becoming more engaged to try to prevent it. But their anger is only shrinking their numbers quicker.
There is a strong parallel to ideological Sanders supporters here. Both groups have a solid core but have trouble communicating to outsiders. Sanders fans have better long term prospects but in short term, neither group gets what it wants
