(RNS) — It was stupid but not weird that Donald Trump tried to tell a Black audience that Kamala Harris only just recently claimed to be one of them.

Stupid, because Harris has never hidden her Black identity behind her Indian one, and because white people should never tell Black people who isn’t really Black. But not weird, because Trump was trading on a deep Judeo-Christian need for things (and people) to belong to clear and distinct categories.

On the Jewish side, take the dietary laws. Animals that have cloven hooves and chew their cud can be eaten. Those who don’t, can’t. Meat must be kept separate, and eaten separately, from dairy products. Pareve foodstuffs — vegan fare plus eggs and fish — can be eaten with both meat and dairy.

Likewise, Israelites were kept apart from other tribes via male circumcision. And a commitment to worship the Hebrew God meant forswearing all other worship. (Remember the Golden Calf?)

That was considered quite the oddity in the Roman Empire, where acknowledgment of the gods of others was normal. But out of respect for other peoples’ customs, the Jews were permitted to refrain from performing acts of emperor worship.

To be sure, the early Christians abandoned major Jewish categorical distinctions. Chapter 10 of the Book of Acts makes clear that restrictions on contacts with gentiles were to be no more in effect than the dietary laws. As the apostle Paul put it in his letter to the Galatians, “There is neither Jew nor Gentile, neither slave nor free, nor is there male and female, for you are all one in Christ Jesus.”

But such effacing of categories didn’t apply to those who had not been baptized. Indeed, like the Jews, the Christians refused to worship other gods — though as a newfangled faith based in no particular people, they were not accorded the Jewish exemption and so from time to time were thrown to the lions.

After the Emperor Constantine’s conversion in the fourth century put the Christians in the religious driver’s seat, it became imperative not only to suppress pagans and heretics but also to insist on a bright line between Jews and Christians. In Antioch, the great church father John Chrysostom denounced the “Judaizing disease” in his flock, writing:

The festivals of the pitiful and miserable Jews are soon to march upon us one after the other and in quick succession: the feast of Trumpets, the feast of Tabernacles, the fasts. There are many in our ranks who say they think as we do. Yet some of these are going to watch the festivals and others will join the Jews in keeping their feasts and observing their fasts. I wish to drive this perverse custom from the Church right now.

In contemporary America, there’s been comparable Jewish agita about those observers of Jewish festivals who call themselves Messianic Jews (aka Jews for Jesus), as if they represent an impermissible spiritual mixing of milk and meat. At the same time, let us note that in some parts of the Jewish community, Buddhism — or at least Buddhist spiritual practices — are considered religiously pareve.

Meanwhile, contemporary American Christians are both accepting of Messianic Jews and ready participants in Passover Seders, whether run by (non-Messianic) Jews or themselves. No doubt, John Chrysostom would have been shocked by such Judaizing, to say nothing of the mixing of the two religions in interfaith marriages, including Kamala Harris’. Similarly, it’s a sign of the declining rigidity of demographic categories in American society that since 2000, the U.S. Census has provided an option for multiple-race identity.

And yet, one need look no further than the current backlash against transgender identity to recognize that many Americans are unsettled by things that don’t fit into long-standing, comfortable categories. Under the circumstances, it seems no accident that the Democratic presidential candidate has chosen as her running mate someone from perhaps the most comfortable and familiar category possible in America: a middle-class white Protestant heterosexual male from the Midwest.

Sure, you say, but what about his outspoken liberalism? Doesn’t that violate the category?

By no means. The foremost liberal in American political history, William Jennings Bryan, was also a middle-class white Protestant heterosexual male from the Midwest. Indeed, like the Great Commoner, Tim Walz hails from Nebraska. And you don’t get more American than that.