President Barack Obama, like many well-read inhabitants of public life, is a professed admirer of Reinhold Niebuhr, the famous mid-20th-century Protestant theologian. And more than most presidents, Obama has tried to incorporate one of Niebuhr’s insights into his public rhetoric: the idea that no society is innocent, and that Americans in particular need to put aside illusions about our own alleged perfection.

The latest instance came at a National Prayer Breakfast, when the president, while condemning the religious violence perpetrated by the Islamic State, urged Westerners not to “get on our high horse,” because such violence is part of our own past as well: “During the Crusades and the Inquisition, people committed terrible deeds in the name of Christ. In our home country, slavery and Jim Crow all too often was justified in the name of Christ.”

These comments were not well-received by the president’s critics — as, indeed, his Niebuhrian forays rarely are. In the past, it’s been neoconservatives taking exception when Obama goes abroad and talks about our Cold War-era sins. This time, it was conservative Christians complaining that the president was reaching back 500 or 1,000 years to play at moral equivalence with people butchering their way across the Middle East.

From a Niebuhrian perspective, such complaints are to be expected. “All men,” the theologian wrote, like to “obscure the morally ambiguous element in their political cause by investing it with religious sanctity.” Nobody likes to have those ambiguities brought to light; nobody likes to have the sanctity of his own cause or church or country undercut.

So the president probably regards his critics’ griping as a sign that he’s telling necessary truths. Indeed, sometimes he is. But the limits of his Niebuhrian style have also grown apparent.

The first problem is that presidents are not historians or theologians, and in political rhetoric it’s hard to escape from oversimplification. You can introduce the Crusades to complicate a lazy “Islam violent, Christianity peaceful” binary, but then a lot of Christians are going to hear an implied equivalence between the Islamic State’s reign of terror and the incredibly complicated multicentury story of medieval Christendom’s conflict with Islam … and so all you’ve really done is put a pointless fight about Christian history on the table. To be persuasive, a reckoning with history’s complexities has to actually reckon with them, and a tossed-off Godfrey of Bouillon reference just pits a new straw man against the one you think you’re knocking down.

The second problem is that self-criticism doesn’t necessarily serve the cause of foreign-policy outreach quite as well as Obama once seemed to believe it would. Early in his administration, especially around his 2009 speech in Cairo, there was a sense that showing Muslims that a U.S. president understood their grievances would help expand our country’s options in the Middle East. But no obvious foreign-policy benefit emerged, and since then Obama’s displays of public angst over, say, drone strikes have mostly seemed like an exercise in self-justification, intended for an audience of one.

A third problem is that Obama is not just a Niebuhrian, but he’s also a partisan and a progressive, which means that he, too, invests causes with sanctity, talks about history having “sides” and (like any politician) regards his opponents as much more imperfect and fallen than his own ideological camp.

The most Niebuhrian presidential speech in modern U.S. history was probably Dwight D. Eisenhower’s farewell address, in which he warned against the dangers of “the military-industrial complex” and “a scientific-technological elite.” It was powerful precisely because Eisenhower was criticizing his own party’s perennial temptations, acknowledging some of his own policies’ potential downsides (he had just created NASA and DARPA) and drawing on moral authority forged by his own military career.

Obama was never going to have Ike’s authority, but he could still profit from his example. The deep problem with his Niebuhrian style isn’t that it’s too disenchanted or insufficiently pro-American. It’s that too often it offers “self”-criticism in which the president’s own party and worldview slip away untouched.

— Ross Douthat is a columnist for The New York Times.