I highly recommend this book. It clearly connects the dots between politics and religion in America.
Jesus and John Wayne: How White Evangelicals Corrupted a Faith and Fractured a Nation https://www.amazon.com/dp/B08C1G1XG3/ref=cm_sw_r_apan_K6AR192ZVFVPJTT46TVC
I'm in the middle of a book that addresses this question exactly. It has probably come up in this sub before.. but.. Jesus and John Wayne by Kristin Kobes Du Mez is pretty fascinating.
If you want to know the actual historical answer to this, I'd suggest starting with Jesus & John Wayne by Kristin du Mez. What's going on here is, Evangelicals have slowly morphed from a twisted racist religious cult into a twisted racist political ideology, and their ideology revolves around the idea of gender roles. To the Evangelical, the role of the man is to be a warrior that protects Christianity and his family and the mother's role is to gratify the man, raise children, and care for the home. Once you realize their central gender role based dogma, the culture wars make a lot more sense, and since the Evangelicals have essentially taken over the Republican party, culture wars have taken over Republican politics. How can protectors of Christianity vote for a north eastern liberal elite abortionist like Trump? Well, they prioritize "tough" warriors for Christianity as the ideal, and Trump was happy to play that role. He's their John Wayne... fighting to empower the white man against the non-white man in Vietnam, in WWII killing Japanese, as a cowboy hunting indians, etc, etc.
The identity of the white Evangelical has also always been closely tied to the debate over slavery... so that's the other ever present American political through-line. It's also how "Libertarianism" started to become a thing in the South. State's rights over the federal government was always actually about state's rights to own slaves. How do you philosophically justify local government over federal government? Libertarianism.
So, what we're seeing is a bunch of people organized around Evangelical toxic masculinity that would describe themselves politically as Republican or Libertarian because of the slavery issue. Slowly, Evangelicalism is taking over, and so they may call themselves Republicans or Libertarians, but none of their positions are based on traditional Republican or Libertarian ideals. Libertarian ideals completely clash with the idea of enforcing gender roles ... like, there's no Libertarian argument closed borders... yet, here we are with so-called Libertarians whining about an invasion of cheap labor ... errr ... Mexicans. What matters now to these folks is "toughness" and being a "christian warrior" in direct contradiction with the actual teachings of Christ. They've merged religion and politics and morphed it to match their disgusting personal beliefs about who men and women ought to be.
I haven't finished reading it yet but so far it's pretty interesting. Jesus and John Wayne