Ryan Burge, a political scientist at Eastern Illinois University, has tracked religious trends for the past 30 years using data from the General Social Survey.
He reports that in 1988, 55.7 percent of Americans were members of traditional, mainstream denominations, 36.6 percent were members of evangelical and born-again denominations and 7.7 percent said they were not religious.
By 2018, membership in traditional denominations had fallen 20 points to 35.5 percent, born-again evangelical church membership had grown by 4.8 points to 41.4 percent, and the share of the nonreligious had tripled to 23.1 percent.
In an email, Burge warned that “in just a few years there will be no moderate Protestants left.”
This has been a windfall for the Republican Party.
As Burge writes: “Almost every predominantly white Protestant denomination — from Southern Baptists and United Methodists to Missouri Synod Lutherans and the Assemblies of God — is solidly Republican” This is apparent in the sea of red in the accompanying chart.