To better understand Mr. Trump’s approach to life, ethics and politics, we should not look to Christ but to Friedrich Nietzsche, who was repulsed by Christianity and Christ. “What is good?” Nietzsche asks in “The Anti-Christ”: “Whatever augments the feeling of power, the will to power, power itself in man. What is evil? Whatever springs from weakness. What is happiness? The feeling that power increases – that resistance is overcome.”

Whether or not he has read a word of Nietzsche (I’m guessing not), Mr. Trump embodies a Nietzschean morality rather than a Christian one. It is characterized by indifference to objective truth (there are no facts, only interpretations), the repudiation of Christian concern for the poor and the weak, and disdain for the powerless. It celebrates the “Übermensch,” or Superman, who rejects Christian morality in favor of his own. For Nietzsche, strength was intrinsically good and weakness was intrinsically bad. So, too, for Donald Trump.

Those who believe this is merely reductionism should consider the words of Jesus: Do you have eyes but fail to see and ears but fail to hear? Mr. Trump’s entire approach to politics rests on dehumanization. If you disagree with him or oppose him, you are not merely wrong. You are worthless, stripped of dignity, the object of derision. This attitude is central to who Mr. Trump is and explains why it pervades and guides his campaign. If he is elected president, that might-makes-right perspective would infect his entire administration.

All of this is important because of what it says about Mr. Trump as a prospective president. But it is also revealing for what it says about Christians who now testify on his behalf (there are plenty who don’t). The calling of Christians is to be “salt and light” to the world, to model a philosophy that defends human dignity, and to welcome the stranger in our midst. It is to stand for justice, dispense grace and be agents of reconciliation in a broken world. And it is to take seriously the words of the prophet Micah, “And what does the Lord require of you but to do justly, and to love kindness and mercy, and to humble yourself and walk humbly with your God?”

Evangelical Christians who are enthusiastically supporting Donald Trump are signaling, even if unintentionally, that this calling has no place in politics and that Christians bring nothing distinctive to it — that their past moral proclamations were all for show and that power is the name of the game.

The French philosopher and theologian Jacques Ellul wrote: “Politics is the church’s worst problem. It is her constant temptation, the occasion of her greatest disasters, the trap continually set for her by the prince of this world.” In rallying round Mr. Trump, evangelicals have walked into the trap. The rest of the world sees it. Why don’t they?