“A Day Without Immigrants” protestors march in the streets outside the state capitol in Austin, Texas in this file photo from February. Drew Anthony Smith/Getty Images

A review of the fundamentals is always worthwhile. For that reason alone, we are all indebted to U.S. Rep. Steve King of Iowa.

“Wilders understands that culture and demographics are our destiny. We can’t restore our civilization with somebody else’s babies,” King wrote via Twitter. ^[10]

The backlash to his statement was swift and included rebukes from several of King’s congressional colleagues. Among them was John Lewis of Atlanta, who called the remarks “bigoted and racist” and more.

“It suggests there is one cultural tradition and one appearance that all of humanity should conform to,” the Atlanta congressman said. Which is true enough, but Lewis’ statement didn’t quite get us to the teachable moment that King’s mischaracterization deserves.

America holds itself out as a nation built around an idea rather than shared DNA or religion — which had been the traditional foundations of European nationhood and to a great extent still are. On this side of the Atlantic, we have been about adding to the gene pool, not refining it.

These topics often come up in families with high school history teachers. Only a few months ago, we were walking out of the movie theater, having watched a Cold War drama called “Bridge of Spies.”

The history teacher among us was giddy. The Tom Hanks character, in a conversation with a CIA agent, had given a succinct speech that the teacher intended to convert to a YouTube video as a way of explaining to students the difference between a constitutional democracy and democratic nationalism.

“My name’s Donovan. Irish. Both sides, mother and father. I’m Irish, you’re German, but what makes us both Americans?” the Hank character asks, then answers himself. “Just one thing … the rule book. We call it the Constitution, and we agree to the rules. And that’s what makes us Americans. It’s all that makes us Americans.”

A declaration that all men and women are created equal is on its face an invitation to immigrants. And so our history has largely revolved around absorption — about changing newcomers and being changed by them. About assimilation and resistance to assimilation.

The first German language newspaper in America, Die Philadelphische Zeitung, ^[11] was published in 1732 by Ben Franklin. German-language journalism thrived, unabsorbed, in the U.S. for nearly two centuries, until World War I.

California’s Constitution of 1849, which brought that state into the Union, was printed in both Spanish and English. ^[12]California would remain a formally bilingual state for 30 years.

The Jim Crow era that followed the Civil War and Reconstruction amounted to white resistance to the assimilation of African-Americans — whose ancestors were brought here unwillingly — into the social and political fabric of the country. While focused in the South, that resistance stretched nationwide.

The civil rights movement of the next century would be its sequel.

As late as the 1950s, hostile Protestants named communism and Catholicism — the latter a mostly European import — as the two greatest existential threats to the United States. Communism is largely gone, and Catholics have finally won acceptance.

If Neil Gorsuch is confirmed as a U.S. Supreme Court justice — his first Senate hearing is Monday — he will be the only Protestant on the nation’s highest bench. The other eight are either Catholic (five) or Jewish (three).

A few days before Steve King sent out his Tweet on what he thought this country was about, an arm of the University of Georgia, the Selig Center for Economic Growth ^[13], published its annual analysis of the state of the multicultural economy in the United States.

Jeffrey Humphreys, the center’s director, is one of the state’s leading economists and has been putting out this particular study since 1990. The report is geared toward businesses that want to reach ethnic and racial minorities in the U.S. with their goods and services.

This year’s headline: In 2016, the $1.4 trillion Hispanic market in the United States was larger than the entire economies of all but 14 countries in the world. Smaller than the gross domestic product of Spain, but larger than that of Mexico. ^[14]

African-Americans still make up the nation’s largest racial minority market, but the buying power of Hispanics — an ethnic group, Humphreys points out — is larger.

In essence, Humphreys matches census data with statistics on economic purchases. He can tell you, for instance, where Hispanic buying habits differ from the rest of America. They spend more on groceries and clothing, but less on tobacco. They spend more on car insurance, but less on health insurance. (Probably because, on the whole, they’re younger. Thirty-five percent are under age 18.)

But Hispanics are like the rest of America when it comes to spending on booze, utilities, furniture, public transportation and grooming products.

In reading this study, I realized that Humphreys has developed some serious data on how racial and ethnic minorities are absorbed into the U.S. mainstream. In some cases, to the point that the data no longer can find them. The Irish, for instance.

“The census doesn’t ask that point. If it did, I could do that. If people could remember whether they were Irish or not,” Humphreys said.

“The thing is, at some point, an ethnic group or even a racial group is going to behave in ways that might not be much different from anyone else. We’re not at that point yet,” he said.

It’s an interesting thought, though. Consumerism as a foundation of national unity. But it will probably not happen.

In walking back his comments, Congressman King said he hoped to see “an America that’s just so homogenous that we look a lot the same.” But that, too, is a misunderstanding of who we are.

Any science student can tell you that homogeneity — whether we’re talking gas molecules or people — occurs only in a closed system that admits no outsiders.

There will always be outsiders pressing to get into the United States, looking to change and be changed. But only if we’re lucky.