Christianity and the “powers that be” have weathered two millennia, their relationship varying by time and place. Pontius Pilate condemned Jesus to the cross. Emperor Constantine converted. Henry VIII broke from Rome and founded the Church of England. In the US, the denominational divides of protestantism helped drive the revolution and provided fuel for the civil war.

In his new book, the Rev Russell Moore opens a chapter, “Losing Our Authority: How the Truth Can Save”, with the words “Jesus Saves”, followed by a new historical tableau: January 6 and the threat Donald Trump and the mob posed to democracy and Mike Pence.

“That the two messages, a gallows and ‘Jesus Saves’ could coexist is a sign of crisis for American Christianity,” Moore writes.

Heading toward the Iowa caucus, Trump runs six points better among white evangelicals than overall. As for the devout Pence, a plurality of white evangelicals view him unfavorably.

Moore is mindful of history, and the roles Christianity has played: “Parts of the church were wrong – satanically wrong – on issues of righteousness and justice, such as the Spanish Inquisition and the scourge of human slavery.” He is editor-in-chief of Christianity Today, a publication founded by Billy Graham. Losing Our Religion offers a mixture of lament and hope. In places, its sadness is tinged with anger. In the south, the expression “losing my religion”, popularized by REM in a 1991 song, “conveys the moment when ‘politeness gives way to anger’,” Moore explains.

Moore’s public and persistent opposition to the election of Trump set him apart from most white evangelicals and would lead to his departure from the Southern Baptist Convention (SBC).

“The man on the throne in heaven is a dark-skinned, Aramaic-speaking ‘foreigner’, who is probably not all that impressed by chants of “Make America great again,” Moore wrote in spring 2016. “Regardless of the outcome in November, [Trump’s] campaign is forcing American Christians to grapple with some scary realities that will have implications for years to come.”

He was prescient. Graham’s son, Franklin, threatened Americans with God’s wrath if they had the temerity to criticize Trump. At the time, Moore was president of the SBC ethics and religious liberty commission. His politics forced him to choose. He opted for Christ and his convictions. He joined a nondenominational church.

His new book is subtitled “An Altar Call for Evangelical America” but it aims for a broader audience. It contains ample references to Scripture, but also to the journalist Tim Alberta, Jonathan Haidt of New York University, Robert Putnam, author of Bowling Alone, and Robert Jones of the Public Religion Research Institute, a nonpartisan group.

Of white evangelicals, Moore quotes Jones: “Their greatest temptation will be to wield what remaining political power they have as desperate corrective for their waning cultural influence.” Welcome to the culture wars, and to what Ron Brownstein of the Atlantic has called the coalition of restoration.

Against the backdrop of rising Christian nationalism and January 6, Moore reads the writing on the wall. He is troubled by the shrinking gap between Christian nationalism and neo-paganism. “The step before replacing Jesus with Thor is to turn Jesus into Thor,” he observes. Moore found the presence of prayers in “‘Jesus’s name’ right next to a horn-wearing pagan shaman in the well of the evacuated United States Senate” disturbing, but not coincidental.

The Magasphere and Twitterverse bolster Moore’s conclusions.

“President Trump will be arrested during Lent – a time of suffering and purification for the followers of Jesus Christ,” Joseph McBride, a rightwing lawyer who represents several insurrectionists, tweeted last March. “As Christ was crucified, and then rose again on the third day, so too will Donald Trump.”

Caesar as deity. We’ve seen that movie before. McBride, however, did not stop there.

Hours later, he tweeted: “JESUS LOVES DONALD TRUMP. JESUS DIED FOR DONALD TRUMP. JESUS LIVES INSIDE DONALD TRUMP. DEAL WITH IT.”

Three-in-10 adults in the US, meanwhile, are categorized as religious “nones”. Only 40% of Americans call themselves Protestant. The Wasp ascendancy has yielded to Sunday brunch and walks in the woods. “The Father, Son and Holy Ghost, they took the last train for the coast,” as Don McLean sang. For some, Trump rallies present a variation of community and communion. A younger generation of evangelicals heads for the door. The numbers tell of a crisis of faith.

“We see now young evangelicals walking away from evangelism not because they do not believe what the church teaches, but because they believe the “church itself” does not believe what the church teaches,” Moore laments.

Predation, lust and greed are poor calling cards for religion. Unchecked abuse within the Catholic church left deep and lasting scars among those who needed God’s love most. Moore notes the Catholic church’s fall from grace in Ireland and posits that “born-again America” may be experiencing a similar backlash, as a powerful cultural institution lacking “credibility” seeks to “enforce its orthodoxies”.

Against this backdrop, Catholicism’s boomlet among younger continental Europeans is noteworthy. Recently, hundreds of thousands converged on Lisbon to hear the Pope. The same demographic helps fuel the resurgence of the Spanish far right. Tethering the cross to the flag retains its appeal.

That said, Jerry Falwell Jr’s posturing as Trump-booster and voyeur didn’t exactly jibe with Scripture. The ousted head of Liberty University, son of the founder of the Moral Majority, allegedly paid a pool boy to have sex with his wife as he watched.

“What we are seeing now … is in many cases the shucking off of any pretense of hypocrisy for the outright embrace of immorality,” Moore writes.

America barrels toward a Biden v Trump rematch. The former president is a professional defendant. The country and its religion sag and shudder. Moore prays for revival, even as he fears nostalgia.

• Losing Our Religion is published in the US by Penguin Random House

• This piece was amended on 14 August 2023 to correctly identify the Public Religion Research Institute as a nonpartisan group.