(CNN) While on a preaching tour in Vermont a few weeks ago, Franklin Graham got an idea: God had helped Donald Trump reach the White House, and now the President needed divine aid again.

Like no President before him, Trump was under attack, Graham said. From Democrats, Republicans, the media, even powers and principalities beyond the human realm. His presidency was in peril, the country at a moral crossroads.

So Graham decided to do what evangelists do: pray, preferably with lots of other people. After calling evangelical allies, he announced plans to name this Sunday, June 2, as a "special day of prayer" to protect Trump from his "enemies."

"We're on the edge of a precipice," Graham said. "Time is short. We need to pray for God to intervene. We need to ask God to protect, strengthen, encourage, and guide the President."

In some respects, the "Pray For Trump" day seems designed to drive positive media coverage of the President, shifting the narrative from a presidency in peril to one buoyed by Trump's most loyal bloc: white evangelicals. Graham himself has no public events planned on June 2, outside of a prayer he'll post on Facebook and a television appearance on Fox News.

Sunday's event is a near-perfect embodiment of political evangelicalism in the Age of Trump: It blends Christian nationalism, the idea that the United States has a special place in God's plans and Trump is God's agent; social media, where it's hard to separate the wheat of grassroots support from the chaff of Russian bots; and it has seriously irked Christians who say Graham and others have sold their souls for a mess of political pottage.

Some have accused Graham of "weaponizing" prayer and turning it into a pro-Trump propaganda tool.

"He's doing so much to discredit the Christian witness," said Peter Wehner , an evangelical who served two Republican presidents in the White House.

Praying for politicians is commonplace in American churches, often occupying a spot in services somewhere between the sermon and the potluck announcements. But Graham's idea is more political -- and more partisan, some Christians say. It's also a significant escalation in white evangelicals' public support for Trump at a critical moment in his presidency.

Just this week, special counsel Robert Mueller spoke publicly for the first time about his 22-month investigation into Russian interference in the 2016 election. Since then, calls for Congress to impeach the President have grown, even from within Trump's own Republican Party.

Graham said the White House is aware of his plans but would not say if he has talked to Trump about them.

As of Thursday, 185,000 people have liked Graham's Facebook post announcing the event and 46,000 more have shared it. More than 300 conservative Christian leaders have pledged to lead prayers for the chief executive.

Graham, the son of famed evangelist Billy Graham and president of the evangelical aid group Samaritan's Purse, has a huge following on social media, where he regularly shares his support for Trump and other conservative politicians. (In contrast, he questioned President Obama's Christian faith.)

But the evangelist said he's never organized an event like this before.

Because of his charity work and family name, Graham carries immense influence over American evangelicals, said John Fea, author of "Believe Me: The Evangelical Road to Donald Trump."

"What he says politically is going to sway how many American evangelicals vote and pray."

But Fea, a historian at Messiah College in Pennsylvania, is among the evangelicals critical of Graham's pro-Trump prayer event.

The historian notes that Graham ended his Facebook post with a dark biblical warning about the array of spiritual forces aligned against contemporary Christians.

"That's a code verse," Fea said. "It sends a clear message to his followers that there is something at work here beyond politics. He's saying that America is under spiritual attack and equating the attacks on Trump with that."

Fears of alienating millennials with partisanship

Graham said he doesn't agree with all of Trump's policies and that God commands Christians to pray for their secular leaders. "If he's a good President, it benefits every American of every race and gender." Still, Graham acknowledged that Trump has been an especially attentive patron to his evangelical base, calling him the "most pro-Christian President in my lifetime."

But other evangelicals have noted the obvious: That Trump's actions as President have not, and likely will not, benefit everyone.

"Nothing in the call to prayer calls Trump to repentance for his many lies, for his support for ruthless dictators around the world, for his obstructions of reasonable congressional oversight, or for the authorization of cruel treatment of asylum seekers at the border," wrote Warren Throckmorton , a psychology professor at Grove City College in Pennsylvania and a close observer of evangelical politics.

Asked how he would answer critics who say that Trump and his evangelical allies are actually a threat to the church, Graham declined to engage the question. "I wouldn't even answer a person like that. I don't think it's valid at all."

But there is some evidence that high partisanship in American Christianity has turned many millennials away from organized religion.

"A leading explanation for the recent surge in the percentage of Americans claiming no religious affiliation is politics," concludes a recent paper by four prominent political scientists. "Liberals and Democrats (are) rejecting organized religion as traditionalist religion becomes associated with conservatism and the Republican Party."

Michele Margolis, an assistant professor of political science at the University of Pennsylvania, said it's too soon to detect a "Trump effect" among contemporary Christians.

But she said that events like Sunday's prayers for Trump strengthen the bonds between the Republican Party and religious right, which will have lasting consequences for both.

"There are religious leaders who are very worried about the downstream effects in 15 or 20 years. They don't think there will be a politically driven exodus from evangelicalism, but there are many evangelicals, particularly younger ones, who really care about the environment and immigration and workers' rights."

Margolis, the author of "From Politics to the Pews: How Partisanship and the Political Environment Shape Religious Identity," recently spent six weeks interviewing pastors and other religious leaders in Alabama.

Some pastors told her that some of their church members threatened to walk out of their churches if they ever prayed for Obama on a Sunday morning, Margolis said. But they are happy to pray for Trump, and likely will this weekend.