Don't get too excited. Religion isn't being pushed off stage. Its being rewritten, or updated, or repaired or prepared for the future. Also the evangelicals are not decreasing in numbers, the very group that you denounce for sponsoring Trump. That is, one group which you say is the cause of the decrease is the group that is not decreasing in numbers.
I have noticed this personally about evangelicals that they have become slightly more catholic over the last twenty years, more flexible, and their churches have spread all over the world. They're not just a USA denomination anymore. Everywhere you go you can find them, microphones and synthesizers piping. They're in Africa, South America, Asia, Australia...etc. They're everywhere.
I agree with
@Faithofchristian that Christians need to figure out how dinosaurs fit with the Bible, and I think that gradually all will. Just as Christians all believe bacteria exist and that the Earth goes around the sun that is what will happen. The RC will adjust. The Liberal churches will stolidly march on and reap the benefits of their meritorious choice to become progressive. The cults will soften and morph or fizzle out. The evangelical churches will notice any innovation and steal it and incorporate it, just as they have been doing with Rock'n roll music, with hypnosis, with stage lighting and sound and personal greeters, and soon they will also be pro evolution, nicer to gays, more pleasant about Halloween and so forth. Its what happens.