The fact that so many Americans listened to and followed those religious nutjobs and they were able to sweep the government with such little effort suggests no such "secularization" ever took place.

They're like people who see some pernicious "gay agenda" infiltrating all aspects of their lives just because they see two gay characters in a sitcom. Their fears are just projection. The power centers of the US have always been biased towards Christian conservatism. It's absurd to claim the US has ever been a truly secular nation when it isn't even possible for a President to get elected without professing Christian belief, because it's impossible to get elected President without the blessing of the deeply Christian south.

The US was 90% Christian and 5% None just 35 years ago. Today it's 63% Christian and 29% None. That seems pretty rapid to me. It has not reached anything close to a majority yet, so the religious still hold great sway. And the perceived threat from their decreasing belief share pushes extremism.