JS: If it’s less about turnout, what about the idea that partisan loyalties have simply changed? You get a “God Gap” among party activists simply because evangelicals are now more loyal to the Republican Party, period. And ditto seculars and the Democratic Party.
RC: I do find that changes in party loyalty matter a great deal, but don’t forget that loyalty changes, while more impressive than turnout changes, are mostly dwarfed by demographic changes. It is true that evangelicals have become more loyal to the GOP over time, and this helps explain why they’re a larger fraction of Republican activists, but loyalty is one of several factors and not the most important one.
Also the Republican Party has always been dominated by religious people. It used to be that these religious people were mostly mainline Protestants, and now they’re mostly evangelical Protestants. A democratic trend among mainline Protestants is an important part of this change — even though such a trend runs counter to God Gap punditry.
And the evangelical trend is a bit more complicated than a God Gap as well. The Republican trend is concentrated among evangelicals in the South. Outside the South, evangelicals have actually trended slightly toward the Democratic Party.