A new kind of Christian nationalism is gaining momentum in the United States. Around the country, evangelical Protestants are deepening their loyalty to President Donald Trump, who announced last October: “You know what I am? I’m a nationalist, O.K.? I’m a nationalist…. Use that word.”

Yet it is not evangelicals but Catholic intellectuals who are helping to lead efforts to capitalize on the opportunity presented by Mr. Trump’s nationalism. Catholic involvement is especially prominent in two recent initiatives. The first was a manifesto published by First Things this March advocating a new style of conservatism that would, among other things, “embrace the new nationalism” and “jealously guard” the space opened up by the “Trump phenomenon.” Among the signatories were Patrick Deneen of the University of Notre Dame, C. C. Pecknold of the Catholic University of America and Sohrab Ahmari, an op-ed editor at The New York Post.

Some have asked us: Why shouldn’t Christians embrace the new nationalism? Doesn’t it amount to patriotism? It does not. To understand why, we need to look more closely at nationalism, at what it is and how it has been understood.

The second initiative was the National Conservatism conference, which took place in July and was organized in part by R. R. Reno, the editor in chief of First Things. Catholic thinkers such as Mr. Reno and Mr. Deneen shared the stage with other politically conservative speakers such as Tucker Carlson of Fox News, the University of Pennsylvania law professor Amy Wax and Senator Josh Hawley of Missouri, a vocal Trump supporter. While theorizing about nationalism, the speakers celebrated the Trump insurgency and praised the president’s instincts on immigration.

In August 2019, we joined two dozen theologians, pastors and academics across denominational lines in an open letter published in Commonweal warning Christians of the dangers of this new nationalism. Here we speak in our own names to examine its intellectual hazards more closely. Some have asked us: Why shouldn’t Christians embrace the new nationalism? Doesn’t it amount to patriotism? It does not. To understand why, we need to look more closely at nationalism, at what it is and how it has been understood.

Political scientists consider nationalism the most widespread ideology in the world today, fusing with movements across the ideological spectrum. But all nationalisms ground state power in the supposedly unique spirit of the people, a common heritage said to precede political rule. Who counts as part of the nation? Nationalists have offered two general answers: an “ethnic” one and a “civic” one.

What is ethnonationalism?

Ethnic nationalism is marked by a sharp division between “us” and “them,” a boundary line drawn in biological, cultural or religious terms. For this reason, ethnonationalists reject multiculturalism. In practice, ethnonationalists have often subjected minorities to disenfranchisement, mass deportations, concentration camps and other attempts to purify “the people” and erect impenetrable borders. The 20th century is filled with terrifying examples.

Such ethnonationalism is clearly incompatible with Christianity. Even leaving aside the horrific violence of purges and camps, the Christian community is called to become constitutively multiethnic. Jesus gathers those of “every nation” (panta ta ethné, Mt 28). While some Christian communities take shape locally and exhibit the cultural characteristics of one ethnicity, Catholic faith requires membership in a global church that transcends ethnic loyalties. Indeed, Jesus identifies himself with the foreigner, the migrant and the prisoner.

Many Trump supporters view their enthusiasm as a matter of simple patriotism. But the uncomfortable truth is that the president’s brand of nationalism is not just patriotism but a version of ethnonationalism. From the start it has been driven by the anxiety that Muslims, Latinos and other non-whites are impossible to assimilate into “American” culture. To cite just one of many possible examples, it is ethnonationalism that underlies Mr. Trump’s statement that congressional representatives, including Alexandria Ocasio-Cortez and Ilhan Omar, should “go back” to the “crime infested places from which they came.”

The new Christian nationalists advance their project under Mr. Trump’s standard, yet claim they are not ethnonationalists like him. But they seem unwilling or unable to articulate a stable civic nationalism that does not elevate one religious or ethnic identity.

What is civic nationalism?

The second variety is civic nationalism, or the view that the people are constituted not by cultural or racial similarities but by shared legal or institutional traditions. Civic nationalism can seem more inclusive and pluralistic—after all, anyone can obey the law or participate in democratic elections. The pertinent question for civic nationalism is not where new citizens come from but whether they are committed to sharing the responsibilities of civic life. If so, then waves of multiethnic immigration might be viewed as renewing the nation and not, as the First Things manifesto suggests, “attempts to displace American citizens.”

But if ethnonationalism is indefensible, civic nationalism is deeply unstable. In practice, civic nationalists have often doubted whether loyalty to legal traditions will be enough to unify a sovereign people. Even the great civic nationalist Jean-Jacques Rousseau urged the Polish government to go beyond patriotism and appeal to ethnic superiority. If Poles were taught that they are inherently better than Russians, he wrote in 1772, “I guarantee that Russia will not subjugate Poland.

That even Rousseau would take such a tack exposes the insecurity that lies at the heart of civic nationalism. Can someone so different from me really love the same civic life? Does society require a more cohesive nationalist glue? Civic nationalists are pulled in two directions, either shedding primordial national identities and shifting toward mere patriotism or drifting back toward ethnonationalism. The more “civic” they become, the less “nationalist,” but the more “nationalist,” the less “civic.”

Here is the problem facing the new Christian nationalists. They advance their project under Mr. Trump’s standard, yet claim they are not ethnonationalists like him. But they seem unwilling or unable to articulate a stable civic nationalism that does not elevate one religious or ethnic identity. They rightly denounce white nationalism from the conference stage. But the alternatives they champion are at present vague and incoherent. Fellow believers should press them to give a better account of how nationalism accords with Christian faith.

Imperfect solutions

To escape ethnonationalism, the new Christian nationalists need to name a principle that unifies the people. There are only a few paths forward here, none of which seem to arrive at their goals.

First, they could affirm ancient republican patriotism or other such allegiances to laws and institutions, with studied indifference to religions and cultures. Clearly, the new nationalists seek a thicker notion of civic identity than this.

Second, they could unify the people through civic religion. And it seems that the new nationalists indeed advocate for this—at least some of the time. In his speech at the National Conservatism conference, for example, Mr. Deneen holds “the nation is not sufficient nor properly conceived if it is not…‘under God.’” Mr. Reno says nations are “appointed” by divine “election,” and their character is given by God as “a chosen people.” When we look closer, however, this religious basis for national belonging is problematic.

On the one hand, if one construed civic rituals broadly, an amalgamated American civic religion must include Muslims, non-theists, therapeutic deists and others. Christians would enjoy no special privilege. As Robert Bellah showed, it was just such a unitarian and decidedly liberal “civil religion” that characterized the U.S. throughout the 20th century.

On the other hand, a narrower civic religion, favoring a particular tradition, introduces other predicaments. The sociologist José Casanova observes that white evangelical Protestants dominated the American right in this way for decades, promising that closer adherence to their religion would ensure the maintenance of social order. But, in the end, politics shepherded the church and not the other way around—and dissenting Christian churches were excommunicated from nationalist orthodoxy, no longer part of the people.

Third, defenders of nationalism might claim that, for all their defects, nations are inescapable, natural realities of human life. Mr. Reno invokes this almost biological “logic of peoplehood” in which “citizenship is akin to membership in a family. It is a given, not a choice.” Mr. Ahmari adopts stronger language, describing nations as “pre-existing sacred communities.”

This notion of natural nationhood seems aimed at shoring up local communities against the tides of unrestrained capitalism, which have indeed decimated civic associations, public life and healthy families. The First Things signatories vow to heed “the cries of the working class as much as the demands of capital” and to oppose soulless affluence. In his address, Mr. Deneen worries about the forces threatening regional identities and mourns their decline.

Up to this point, and worryingly, the only localisms Christian nationalists have consistently defended are conservative, Christian and (de facto) white.

Respecting America’s diverse cultures

We find much to agree with here. The Christian nationalists offer a crucial insight: Affections for local solidarities must be rebuilt on something firmer than the sands of libertarianism, consumerism and popular culture. There is something in this that resonates with Catholic social teachings on subsidiarity.

Unfortunately, nationalism is no solution to this problem. Nationalist consciousness is not a local or natural affection but a monoculture engineered by modern states. This is a well-known fact of the historical record. For instance, peasants in 19th-century France did not consider themselves French nationals until Parisian elites imposed their modernizing agenda upon them. Like Mr. Deneen, the peasants wanted to foster what the historian Eugen Weber called “village particularisms.” But it was nationalists who, through state coercion, taught French peasants to love the abstraction of the “nation.” Similar transformations occurred across Europe from Prussia to Italy.

What we ought to learn from this is that nationalist states promote not a variety of local cultures but a single, state-wide monoculture. And the new nationalists have not clarified how the nationalism they espouse can protect or promote religious and cultural differences. Even more disquieting is that most of their references to multiculturalism are pejorative. Mr. Reno ominously warns that his nationalism ought to “troubl[e] those who aspire to a multicultural regime.” These theorists owe their fellow Christians an explanation of how the manifold richness of American communities would be respected in their nationalist vision.

Whose neighborhoods, congregations and families would thrive under such nationalism? New Agers in Boulder? Latinos in El Paso? Muslims in Detroit? Lesbians in Oakland? Mr. Reno states that “our nation tugs at our hearts, and a national conservatism is ordered to the protection…of a shared way of life.” But he fails to explain who he includes in his state-privileged modus vivendi. Mr. Ahmari correctly states that “there is nothing Christian in obliterating human difference and particularity.” But he misses the fact that nationalism negates local particularity in favor of monoculture.

To be sure, some forms of multiculturalism could evolve into an ideological monoculture of their own, suppressing other visions of human flourishing and even elements of Christian life. Anxious to avoid this fate, the new nationalists devote their energy to protecting localism from “cosmopolitanism.” But nationalist ideology is the wrong tool for this work. Up to this point, and worryingly, the only localisms they have consistently defended are conservative, Christian and (de facto) white. Until the nationalists make up their minds about American diversity, critics will wonder if their enthusiasm for local particularism empowers one particularism at the expense of others.

A prominent textbook warns that if “Christians have sometimes unwittingly tied their Christianity to the nation-state, they have done so along certain set grooves of history that we too often forget…. By remembering what nationalism has cost us in the past, we have a much better chance of understanding what has gone wrong and how we might resist its pull in the future.” The author of these wise words is C. C. Pecknold, who also signed the First Things manifesto. Mr. Pecknold is right: It is easy to forget.

Nationalist states do not promote a variety of local cultures but a single, state-wide monoculture. And the new nationalists have not clarified how the nationalism they espouse can protect or promote religious and cultural differences.

What nationalism in action looks like

Catholic intellectuals cannot in good faith theorize a new nationalism in a vacuum, safely sealed away in conference rooms or magazine pages. The nationalists themselves invoked the “Trump phenomenon” as the occasion for their movement. If they wish to draw a sharper line between themselves and Trump’s ethnonationalism, we would welcome it.

But until they do, the new nationalism will be defined not primarily by their theories but by the Trump administration’s actions at the border: inflicting profound and needless psychological damage by separating infants from their parents; denying soap, tampons and flu vaccines to those in custody while asylum cases wend through the courts; suspending the Flores agreement in order to render detentions indefinite; and deporting children with cancer diagnoses to certain death. This is also what nationalism means.

As a concrete political reality, the new nationalism has no enthusiasm for civic localism. Its leader does not actually defend diverse, local families and diverse, local communities, but only a racialized, nostalgic monoculture of white Christian dominance. Unless and until sharper distinctions are drawn, “nationalism” will remain tied to the Trump administration’s increasing violence against vulnerable minorities. From a unity deeper than citizenship, that of baptism, we implore our fellow Christians: Join us in denouncing this violence, and help us understand what distance is left between that nationalism and yours.

David Albertson is an associate professor of religion at the University of Southern California. He is the author most recently of The Geometry of Christian Contemplation: Measure without Measure and the executive director of the Nova Forum for Catholic Thought.

Jason Blakely is a professor of political science and political philosopher at Pepperdine University in California. He is the author most recently of Lost in Ideology: Interpreting Modern Political Life and a senior fellow at the Nova Forum for Catholic Thought.