Not too long after Donald Trump took office in 2017, a reporter told me about a series of interviews she had conducted with Mr. Trump’s evangelical supporters. These folks explained their enthusiasm, she said, for the new president with explicit references to the Bible. A common theme was President Trump is like King David. Morally flawed, of course, but still used by God to accomplish good things for the cause of righteousness.

As an evangelical critic of President Trump, I do not share their admiration for our commander-in-chief, but in some respects, I do appreciate the biblical point they are making. I certainly believe that God does use people who are seriously flawed in their public lives to accomplish his purposes for our collective existence. And David did accomplish many good things as the king of Israel. And he certainly did some very bad things during his reign—not the least being his double sin of having an affair with a married woman, Bathsheba, and then using his kingly powers to ensure that her husband was killed in the line of battle.

But there is another important voice in David’s story: the Prophet Nathan. When Nathan learned of David’s affair with Bathsheba, he came to David to make it clear that this was unacceptable to the Lord. In what was surely a move that put his own life at risk, Nathan preached a sermon to the king in which he told a story about a person who used his power to commit a serious sin. Then he drew the parallel to what David had done.

I was reminded of Nathan the Prophet after the recent Christianity Today editorial calling for Trump’s removal from office. That call honored a crucial element in the King David story. In pronouncing a blessing on David’s kingship, the Lord did not expect David’s subjects simply to ignore the impact of his sinful behavior on his ability to lead. Published just before Christmas, retiring Editor-in-Chief Mark Galli’s words were a clarion call to Christians that the president has abused his power and must be called to account. “But the facts in this instance are unambiguous: The president of the United States attempted to use his political power to coerce a foreign leader to harass and discredit one of the president’s political opponents,” Galli wrote. “That is not only a violation of the Constitution; more importantly, it is profoundly immoral.”

At the risk of losing subscribers and harming their publication—which was attacked by the president himself on Twitter—Christianity Today delivered an important message. The prophetic editorial has been the occasion for renewed charges that Trump’s evangelical supporters have allowed political concerns to override concerns about presidential character. The president’s supporters do not dispute claims that he has said and done some highly offensive things. Instead, they tell us that we are obliged as citizens to support leaders who promote what we consider to be crucial political goals. And in this, they tell us, President Trump—whatever else we might say about him—has shown himself to be on our side. Christianity Today had a response to this as well: “To the many evangelicals who continue to support Mr. Trump in spite of his blackened moral record, we might say this … Consider what an unbelieving world will say if you continue to brush off Mr. Trump’s immoral words and behavior in the cause of political expediency.”

Many evangelical leaders have been very un-Nathan-like in their relationship with President Trump. The president, one of them has told us, is still “a baby Christian.” Others have argued that a focus on the president’s misdeeds detracts from the way Trump is furthering causes that are important to people of faith. We are warned that evangelicals who express our disappointment in his behaviors threaten our own political influence. In American politics, we have been told, we are not voting for candidates for sainthood but for leaders who can promote concerns that are crucial to the evangelical cause. The result is that moral teaching is made subservient to political expediency.

My point here is not a partisan one about Donald Trump. All Christians, on the left or on the right, need to be aware of the ways in which our assessments of a public leader’s character are often strongly influenced by our political biases. As sinners, we are constantly tempted to frame public discussions in ways that promote our partisan causes.

My argument here is not directed to those who might insist that Donald Trump has not been especially sinful in his use of power. I would strongly disagree, but that is a different kind of argument. What I am arguing against here is the views of those Christian leaders who offer political reasons for not drawing attention to the president’s misdeeds. They offer no defense of the behavior in question—but they neither do they offer any reprimands.

The prophet Nathan saw things differently. My educated guess is that if David were running for re-election as king right after the Bathsheba affair, Nathan would not have voted for him. The prophet insisted that worshipers of the true God should hold leaders accountable for serious violations of their obligations as leaders. Moreover, King David responded to Nathan’s critique by repenting of his sin, and by seeking forgiveness. I have seen no such remorse from the president.

When Trump’s evangelical supporters tell us that in presidential elections we are not voting for candidates for sainthood, I agree. I have been voting in elections for more than a half-century now, and I have frequently cast my ballot for folks whose personal lives fall far short of sainthood. I have never insisted that candidates for public office get high scores in “What would Jesus do?” tests. But Christians do have a responsibility to promote the cause of moral leadership in public life. And I do want Christian leaders to be guided in their decisions by keeping the “What would Nathan do?” question clearly in mind. The writer of the Christianity Today editorial has now done just that in the case of President Trump. I am grateful for the prophetic message.

Richard Mouw is president emeritus and professor of faith and public life at Fuller Theological Seminary.