Orthodox Jews and orthodox Christians may view each other as natural allies.

Large segments of both groups tend to be social conservatives with a shared belief in a divinely sanctioned model of marriage and family. Both are unwavering in their support for Israel. And the staunchest religious conservatives, Christian and Jewish, are also united in opposing liberalism — often caricatured as moral relativism or anti-religious secularism — which they consider an existential threat. On a range of issues, many within these two faith communities stand on common ground.

But given the unique relationship between Christianity and Judaism, common ground is not a simple thing. In fact, it is a minefield, especially for Orthodox Jews. The American Orthodox rabbinate sets strict guidelines for interfaith dialogue and forbids official discussion on matters of belief.

Yet on the battlefields of the culture wars, some Orthodox Jews have found common cause with conservative Christians. Behind the burgeoning partnership is the idea that despite their religious incompatibility, Jews and Christians can agree on the content of a fundamental divine morality. The first principle of this ideology is the “Judeo-Christian tradition.”

Politics aside, the idea is flawed. While Christianity’s deepest roots are in Judaism, the Judeo-Christian tradition is historical fiction. As religious communities, Jews and Christians effectively parted ways by the middle of the first century. Since then, in theology, religious practice, and historical experience, they have been defined more by their differences than their commonalities. (In a 1969 essay in Commentary titled “The Myth of the Judeo-Christian Tradition,” Arthur A. Cohen called it “a myth which buries under the fine silt of rhetoric the authentic, meaningful, and irrevocable distinction which exists between Jewish belief and Christian belief.”)

A corollary to the Judeo-Christian tradition is the notion of a common moral code called “Judeo-Christian ethics” or “biblical values,” as though it were an essential Judeo-Christianity reduced to its bare bones. And this too is a myth. Such an ethic never existed in practice and cannot arise naturally from the history of religion. To manufacture one would violate the integrity of both faiths.

To begin with, from which Bible and from whose extra-biblical tradition should Judeo-Christian ethics be taken: The Hebrew Scriptures and the Talmud? The Gospels and the Church Fathers? All of the above? The Tanakh and the Old Testament may contain the same verses but each is wrapped in a distinct prophetic and moral tradition often unrecognizable to the other. Even the Ten Commandments, viewed through layers upon layers of interpretation and practice, fails the test of commonality.

The Judeo-Christian tradition is a uniquely American idea with a history of its own. In the postwar period, it was intended to foster cultural inclusiveness, in much the same way that a transdenominational American “civil religion” — with its own mythology, holidays, martyrs, villains, and saints — lowered cultural barriers for the children of European immigrants. Americans were to be one nation under a nonsectarian God.

“Judeo-Christian” has come to mean something else. The expression could simply reflect a traditional orientation towards American culture. But it might also be an exclusionary label for a society that tolerates all religions while it is dominated by two (more precisely: a blend of two, not necessarily in equal measure). And it may be a euphemism — a veiled claim that the United States is, once was, or should be, a great Christian nation (the “Judeo” part of “Judeo-Christian” sometimes feels like an afterthought; a fig leaf designed to conceal a socially unacceptable description of our national character).

Taking the idea a few steps further, 21st-century nativists have weaponized “Judeo-Christian” in their bid to purge America of any influence outside of its “European” or “Western” heritage. It’s not hard to guess which ethnic and religious minorities are excluded from that vision of America.

Religion is a primary source of personal and social identity and will inform the moral choices of religious Americans. But religion need not be the sole basis of moral identity or moral fellowship, especially in the United States. A much wider moral circle encompasses Americans of all religious stripes. We are a nation of traditional American values that are a legacy of the secular (but not godless) Enlightenment as much as revealed religion. Like American democracy itself, our common civic values transcend religious divisions. Christians and Jews — along with members of all faiths and those who profess none — can find unity in the values, norms, laws, and institutions of our great Republic.

To that, let every patriotic American say Amen.