This article is another theory on the improbable alliance between evangelical Christians and Donald Trump, the formerly secular, thrice married, "baby Christian" who had affairs with porn stars: https://www.alternet.org/evangelical-historian-explains-how-christians-came-put-trump-ahead-jesus
The article is by Paul Rosenberg, originally on Salon.com. It is a review of a book by a formerly evangelical historian names John Fea, called Believe Me: The Evangelical Road to Donald Trump.
Fea argues that white evangelicals are concerned with power, nostalgia, and fear of the future. He discusses the election of Trump on several timescales. The most recent events leading to the 2016 election caused the selection of Trump by evangelicals in spite of some much more likely candidates, including Marco Rubio, Mike Huckabee, Ben Carson, and Ted Cruz. Fea argues that these likely candidates understood evangelicals too well. They tried very hard to frighten the evangelicals about the consequences of the Obama Administration and their loss of political power. The evangelicals were so alarmed that they decided a strongman was needed to restore their power, and Trump fit the bill better than Rubio, Huckabee, Carson, or Cruz. Trump also had the background of his birtherist attacks on Obama as a racist introduction.
Fea also discusses Christianity as it's evolved from further into the past. Rosenberg adds comments from Seth Dowland from his essay for Christian Century, “American evangelicalism and the politics of whiteness.” American Christianity was deeply divided by the Civil War, and it remains divided. The church became segregated and divided between northern white Christians, southern white Christians, and the black churches. Each strain developed its own culture and concerns. Black Christians were more interested in Christian hope. Whites, especially southerners, gravitated toward fear. They felt that they needed political and financial power, and they didn't seem to trust God to sort out human affairs.
Rosenberg points out that Fea's book seems to disregard that evangelical leaders have learned that politics and religion don't go well together. This is something that the American Founders tried to guarantee with the First Amendment. But white evangelicals still seem to be trying to hang on to political power, regardless.