In fairness, that's 1985. Arguably the modern phenomenon of fundamentalist evangelical protestants being a big force in US politics only _really_ got going after Row v Wade; it was a much easier thing to predict in 1985, when that book was written, than in the early 70s. In the 70s, if anything, people would've been more worried about 'new religions'; this was the timeframe in which Hubbard was wiretapping the IRS and so on.

I think sci-fi reflects that; 60s and 70s sci-fi, where it touches on religion as a threat at all, concentrates on cults. You start seeing fundie-christians-as-threat stuff, like Handmaid's Tale, a bit later.

EDIT: However. Honourable mention to Heinlein, who did this in _1940_: https://en.wikipedia.org/wiki/%22If_This_Goes_On—%22 (played very straight; crazy preacher becomes US president in 2012, no elections thereafter) - possibly important context is that there had been a surge in televangelism in the 1930s.