Mr. Trump won a plurality of evangelical votes in each of the last three Republican contests, in New Hampshire, South Carolina and Nevada. He won the glowing endorsement of Jerry Falwell Jr., the president of Liberty University, who has called him "one of the greatest visionaries of our time." Last week, Pat Robertson, the founder and chairman of the Christian Broadcasting Network, told Mr. Trump during an interview, "You inspire us all."

If this embrace strikes you as discordant, it should. This visionary and inspiring man humiliated his first wife by conducting a very public affair, chronically bullies and demeans people, and says he has never asked God for forgiveness. His name is emblazoned on a casino that features a strip club; he has discussed anal sex on the air with Howard Stern and, after complimenting his daughter Ivanka's figure, pointed out that if she "weren't my daughter, perhaps I would be dating her." He once supported partial-birth abortion and to this day praises Planned Parenthood, the nation's largest abortion provider. He is a narcissist appealing to people whose faith declares that pride goes before a fall.

Mr. Trump's character is antithetical to many of the qualities evangelicals should prize in a political leader: integrity, compassion and reasoned convictions, wisdom and prudence, trustworthiness, a commitment to the moral good.

When Bill Clinton was president, evangelicals ranked moral probity high on their list of leadership qualities. Supporters of Mr. Trump, a moral degenerate, justify their support by saying we're electing a president rather than a pastor. Why a significant number of evangelicals are rallying round a man who exposes them as hypocrites is difficult to fathom.

Part of the explanation is that many evangelicals feel increasingly powerless, beaten down, aggrieved and under attack. A sense of ressentiment, or a "narrative of injury," is leading them to look for scapegoats to explain their growing impotence. People filled with anger and grievances are easily exploited. As the great Christian apologist C. S. Lewis wrote, "We must picture hell as a state where everyone is perpetually concerned about his own dignity and advancement and where everyone has a grievance."

Enter Donald Trump, alpha male.

Mr. Trump's evangelical supporters don't care about his agenda; they are utterly captivated by his persona. They view him as the strongest, most dominant, most assertive political figure they have ever seen. In an odd bow to Nietzschean ethics, they respect and applaud his Will to Power. And so the man who openly admires tyrants like Vladimir V. Putin and praised the Chinese crackdown in Tiananmen Square because it showed "strength" has become the repository of their hopes.

Set aside the fact that Mr. Trump is a compulsive and unrepentant liar. Set aside, too, that he has demonstrated no ability for statecraft or the actual administration of government and has demonstrated much incompetence at business to boot.

Mr. Trump's approach to life is not new. In "The Republic," Plato writes of Thrasymachus debating Socrates over the meaning of justice. Thrasymachus, a cynical Sophist, insists that justice has no intrinsic meaning but is merely a pretty word for what is in the interest of the stronger party. Life is a competition to get more money and more power; that is what defines success. "Injustice, if it is on a large enough scale, is stronger, freer, and more masterly than justice," he argues.

Almost four centuries later, a carpenter from Nazareth offered a very different philosophy. When you see a wounded traveler on the road to Jericho, Jesus taught, you should not pass him by. "Truly I say to you," he said in Matthew, "to the extent that you did it to one of these brothers of mine, even the least of them, you did it to me."

At its core, Christianity teaches that everyone, no matter at what station or in what season in life, has inherent dignity and worth. "Follow justice and justice alone," Deuteronomy says, "so that you may live and possess the land the Lord your God is giving you." The attitude of Thrasymachus is foreign to biblical Christianity. So is Trumpism. In embracing it, evangelical Christians are doing incalculable damage to their witness.

Peter Wehner, a senior fellow at the Ethics and Public Policy Center, served in the last three Republican administrations and is a contributing opinion writer