This was my undergrad dissertation! So thrilled it's finally useful. TLDR: The South is religious. Carter politicised religion. Reagan moved religion to the Right. Bush merged religion with the Right. Today, the two are inextricable.

The first Republican sweep of the South was the 1972 election under Richard Nixon. This was an anomaly, reflecting how unsuitably McGovern was as a presidential candidate and the chaos of the Democratic Party following the assassination of Bobby Kennedy.

In 1976, Jimmy Carter found himself facing Gerald Ford, and a roster of talented Democrats like Morris Udall. Carter was a devout Southern Baptist Texan, running on a platform emphasising his inexperience in the wake of the Watergate Scandal. Ford, on the other hand ran the "Rose Garden" strategy where he portrayed himself as a master administrator and experienced politician. This paid off well and Ford had secured a comfortable lead in the polls.

Almost by accident, Carter's strategists discovered a new avenue of bringing in votes, particularly in the historically Democrat but very religious South. In Kenosha, Carter remarked, "The most important thing in my life is Jesus Christ," which was exceedingly well-received in polls. The religious campaign kicked off into action, with books published by charismatic preachers like The Miracle of Jimmy Carter, and full-page ads taken out in main papers with the tagline "Only JC can save America" a pun on Jesus Christ of course. The largest televangelists in the nation, Jerry Falwell and Pat Robertson openly held "I Love America" rallies in 141 cities mostly in the South, endorsing Carter and rallying citizens to "take a stand against the forces of evil at work around the country." Even then, Carter only won on a hairline.

The religious vote had never been a thing, JFK was Catholic for example, and the Southern Baptists in particular were militant supporters of the separation between Church and State. The Southern Baptist confession of faith even contained the dictum, "The Church shall not resort to civil power to carry on God's work", which is why their leadership repeatedly refused to condemn abortion in 1971 and 1974. It was widely seen as impossible anyway, given there was no unified religious position. The left was led by religious leaders like Martin Luther King at the same time that white supremacists like Strom Thurmond were being fielded by the Democrats. In 1976, chief Republican spin doctor David Keene remarked, "I expect there's a potential source of some vote power with evangelicals, but I don't know how it can be demonstrated."

The problem was that Jimmy Carter was a true Southern Baptist, and felt very uncomfortable with what he saw as a blurring of the lines between Church and State. He openly declared early in the race, "No one should vote for me because I am Christian," and yet they did. People like Falwell imagined Carter would champion their evangelical crusade for the moral soul of America, but his political principles refused to regulate individual morality, which led to a permanent falling out. When Carter nominated leading feminist Bella Abzug to the 1977 International Women's Year conference, Robertson and Falwell sent 7,000 of their own delegates calling it, "the war between God and the Devil." Pastors like Bob Jones III pulled together massive petitions and made ads with taglines like "If the Present is against homosexuality, let's see some evidence." In response, Carter, who was obsessed with human rights could only offer, "While homosexual unions are not normal interrelationships, I don't feel that society, through its laws, ought to abuse or harass the individual." This triggered the 1977 Anita Bryant rallies, where the famous singer led protests of tens of thousands of people that culminated in an anti-gay referendum in Miami.

When 1980 rolled around, divorced playboy Hollywood actor Ronald Reagan took the opposite strategy, putting aside his own personal views to swing the entire religious establishment. Appearing at the 1980 Religious Roundtable, he called for creationism in schools, described abortion as "the taking of human life", and in an amazing reversal, condemned "the increasing tendency of the state to interfere with religion". Falwell and Robertson were in love, calling him "God's instrument in rebuilding America", this swung the entire Southern vote, but eventually Reagan didn't really give a shit. Buoyed by success in the Cold War, there was no need to sacrifice political influence to evangelicals. The Republicans now held the means to command the religious vote (i.e. the South) but no longer had the will or need. In any case, the damage was done. The more religious states like Texas would never again vote Democrat, and most of the others exposed the propensity of the South to swing based on religion.

Enter Bush Junior. Unlike Reagan, Bush was a born-again true believer who has proclaimed "Jesus Day" in Texas, pressured his staffers into "attendance at weekly Bible studies, which was not compulsory, but not quite uncompulsory either", advocated the use of federal money for religious charities, and completely off topic answered a question on his most important political philosopher with "Christ". The Republicans revived the full paraphernalia of the Reagan campaign to run the most divisive campaign yet, which ended with 84% of the white evangelical vote while losing 96% of the Black vote and 75% of the secular vote. As President, Bush was the gift that kept giving. He appointed two anti-abortion judges to the Supreme Court, denied funding for family planning and feminist movements, and offered federal funding to Churches. When 9/11 rolled around, the administration was making statements like "Radical Islam is the Communism of the 21st century, Christians have a unique and vital role to play in the historical drama that is unfolding." During the Iraq War, he made a speech referring to Iraq as "Biblical Babylon" and himself as "a messenger of His will in his Holy War." In the 2008 election, McCain continued this principle with the statement, “I have a purpose, and that purpose, I think, is to live a life based on Judeo-Christian principles and honor and integrity.” He also swept the South despite losing the elections. And more recently, Trump, well we all know that story.

Sources:

1. Feldman & Frederickson (2015) - The Great Melding: War, the Dixiecrat Rebellion, and the Southern Model for America's New Conservatism

2. Flippen (2011) - Jimmy Carter and the Rise of the Religious Right

3. Hankins (2002) - Uneasy in Babylon: Southern Baptist Conservatives and American Culture

4. Mason (2009) - Reading Appalachia from Left to Right

5. Smith (2006) - Faith and the Presidency

6. Steding (2014) - Presidential Faith and Foreign Policy

7. Williams (2010) - God's Own Party: the Making of the Christian Right