... Why, dating to the 2016 election, have conservative evangelicals steadfastly supported a president whose crass, vulgar conduct and reported affairs seem to be the antithesis of what they’ve preached for decades?

Some evangelical voters genuinely like Trump, for the same reasons that his other supporters like him: He speaks his mind, he’ll build a wall, he’ll drain the swamp. And, importantly, he was not Hillary Clinton — a pro-choice Democrat who has been the subject of conservative ire for over two decades.

But, more significantly, Trump benefited from a political alliance 40 years in the making.

A look at the country’s largest lobbying organization for conservative women — the distinctly evangelical Concerned Women for America (CWA) — reveals that evangelical support for Trump is the byproduct of decades of political lessons that have taught evangelicals that only a firm alliance with the Republican Party can produce the legislative changes that can save America.

The prominent evangelical author Beverly LaHaye founded Concerned Women for America in 1979 to prove that “the feminists do not speak for all women in America.”

This was an important historical moment for conservative evangelicals like LaHaye. Although right-leaning Christians had been active in politics throughout the 20th century, the late 1970s saw the emergence of a newly cohesive and newly self-aware movement that would come to be known as the New Christian Right.

It was also during this period that conservative Christians and the Republican Party found one another.

The GOP had only recently established itself as the party of the right — thanks to the efforts of Richard Nixon to recruit conservative Southerners to the party. The 1964 Civil Rights Act and the 1965 Voting Rights Act had loosened this population’s century-long allegiance to the Democratic Party, and Nixon’s appeal to a “silent majority” of voters captured the dissatisfaction that many white Americans felt about the civil rights movement, anti-Vietnam War protests and proliferating identity movements on the left.

By 1972, the GOP was on its way to becoming the party of the new social conservatism. ...