Tom Gjelten, a correspondent for NPR News, is author of “A Nation of Nations: A Great American Immigration Story.”

Immigrants waiting to be transferred, Ellis Island ON October 30, 1912. (Underwood & Underwood / Library of Congress)

Rep. Steve King’s tweet this past week in defense of Geert Wilders, the anti-immigrant Dutch politician, won the Iowa Republican praise from white supremacists but a put-down from his colleagues. “Wilders understands that culture and demographics are our destiny,” King wrote. “We can’t restore our civilization with somebody else’s babies.” Jeff Kaufmann, the Iowa Republican chairman, appeared to speak for the consensus in answering the notion that children of foreign-born parents are not quite American. “We are a nation of immigrants, and diversity is the strength of any nation and any community,” Kaufmann said.

But in one small way, King was on to something: Immigration does change a nation’s culture. It has altered America’s national identity, and the transformation has been stressful.

Fifty years ago, only about 5 percent of the U.S. population was foreign-born, and the newcomers were almost entirely from Europe. The 1965 Immigration and Nationality Act opened America’s doors to people of all nationalities, with dramatic effect. By 2010, immigrants made up about 13 percent of the population, and 9 of 10 were coming to America from outside Europe. These Asian, African, Middle Eastern and Hispanic immigrants bring rich diversity to American music, architecture, cuisine and sports; they contribute mightily to growth and innovation in science, technology, medicine and other sectors of the economy.

They have also forced us to revise our thinking about what it means to become American. Gone is the “melting pot” idea, with its assumption that immigrants can become indistinguishable from natives. This is not a concession to some politically correct celebration of differences; no matter how willing Ni­ger­ian Americans or Korean Americans may be to melt into the broader population, they cannot change the color of their skin. Patriotic Muslims and Sikhs can’t do anything about a religious heritage that does not fit with the notion of a Christian America.

The more diverse immigrant influx of recent decades has brought new life to an old debate over America’s national identity. From the time of its founding, the United States has been a nation defined, at least in theory, by a political ideal rather than by a particular people. John Quincy Adams said that Americans “look forward to their posterity rather than backward to their ancestors.” The French travel writer Alexis de Tocqueville observed that Americans in this regard were “quite exceptional” compared to Old World Europeans.

That understanding of the American nation was not really tested, however, because in practice the country existed only as a slightly more open European state. Diversity in early America meant the presence of German immigrants in addition to the British and French who had arrived earlier. The limits of that idealized identity became apparent when the immigrant pattern diverged from the original profile, first with the arrival of a largely poor Irish population, then with Chinese laborers, and finally with a big influx of Southern and Eastern Europeans.

Each new wave was met with hostility. A Massachusetts official, writing in 1857, informed the state legislature that the Irish immigrant population was characterized by “wretchedness, beggary, drunkenness, deceit, lying, treachery, malice, superstition.” Chinese immigrants in California competed with white, Mexican and black workers and faced violent attacks as a result.

The Harvard-trained lawyer Prescott Hall, co-founder of the Immigration Restriction League, posed this question in 1897: “Do we want this country to be peopled by British, German, and Scandinavian stock, historically free, energetic, progressive, or by Slav, Latin, and Asiatic races, historically downtrodden, atavistic, and stagnant?” Congress offered an answer in 1924 by enacting national-origin quotas, allowing Northern and Western Europeans virtually unlimited entry while restricting immigration opportunities for Southern and Eastern Europeans and effectively excluding Asians, Africans and Middle Easterners.

That policy was hugely disappointing to those who clung to a more idealized definition of the American nation, like Maurice Samuel, a novelist who was born in Romania but raised in Britain and the United States. “If America had any meaning at all,” he wrote, “it lay in the peculiar attempt to rise above the trend of our present civilization — the identification of race with State.”

In 1952, after Congress passed a new immigration law upholding the national-origin quotas and then overrode a veto, President Harry Truman established a commission to review the country’s immigration policy. The commission’s report, titled “Whom We Shall Welcome,” concluded that “national uniformity” was neither desirable nor necessary, because “an outstanding characteristic of the United States is its great cultural diversity within an overriding national unity.”

When the national-origin quotas were abolished 13 years later, the United States was ready to test whether it could finally live up to its founding promise as a nation defined independently of race, ethnicity, religion or national origin. Within a few decades, the challenges were apparent: Not only were the post-1965 immigrants coming from different parts of the world, there were many more of them. Immigration over the preceding four decades had slowed to a trickle, giving the assimilation process more time to work. Now the phenomenon was accelerating. Separate immigrant identities were constantly reinforced by the arrival of new people from the same ancestral lands. The liberal historian Arthur Schlesinger worried about the rise of a “cult of ethnicity” that “belittles unum and glorifies pluribus .”

It was time to get more precise in the definition of a core civic culture, and it was precisely the big immigrant influx that prompted the reflection. Political scientist Seymour Martin Lipset advanced de Tocqueville’s notion of American exceptionalism with his proposition that becoming an American is “an ideological act” akin to adopting a new “political religion” whose creed includes five essential ideas: liberty, egalitarianism, individualism, populism and a laissez-faire approach to governance and daily life.

How much cultural diversity could be tolerated under such a broad conception of American identity was not immediately clear. The surge in non-European immigration inevitably produced some backlash. A 1983 direct-mail solicitation for an English-only campaign produced 300,000 responses within a few months. When bakeries in formerly white neighborhoods switched from donuts and cheesecake to churros and pan dulce, when some Korean shop owners treated their African American customers rudely, when Somali high school students insisted on sitting together in the lunchroom, community solidarity suffered, at least in the short term. Native-born Americans noticed these changes.

In his 2004 book, “Who Are We? ,” Harvard University political scientist Samuel Huntington argued that America was “Anglo-Protestant” at its core and that the unity of the country was jeopardized by immigrants who did not identify with that culture. “Throughout American history,” he wrote, “people who were not white Anglo-Saxon Protestants have become Americans by adopting America’s Anglo-Protestant culture and political values.”

Whether that had really happened or was even possible was debatable. “A nation of more than 130 cultural groups cannot hope to have all of them Anglo-Saxonized,” argued Molefi Kete Asante in his book “The Painful Demise of Eurocentrism.” Trying to do so, he argued, would only alienate minorities and deepen disunity.

For the Steve Kings of America, the solution may simply be to stop accepting “somebody else’s babies” and return to considering the national origin of immigrants as a factor in whether they should be allowed entry. In a Phoenix campaign speech, Donald Trump argued, “It is our right as a sovereign nation to choose immigrants that we think are the likeliest to thrive and flourish and love us.”

Implicit in such comments is the suggestion that nondiscriminatory immigration is too much of a burden on a nation’s core culture, even in such a broad-minded country as the United States of America. One reading of the 2016 election is that this was the verdict of American voters.

But there is also a more hopeful assessment. The surge of non-European immigrants over the past 50 years has undeniably changed the culture, but with the effect of strengthening it, not weakening it. America today is a more resilient nation precisely because of its experience with immigration. In comparison with Western European countries that have also received large numbers of immigrants, America has proved to be more capable of absorbing and successfully integrating a diverse population.

There is a danger of overanalyzing the significance of Trump’s election, especially with regard to Americans’ attitudes toward immigrants. An abundance of survey data makes clear that Americans are becoming more receptive of the foreign-born, not less. In 1994, according to the Pew Research Center, 63 percent of Americans saw immigrants as a burden on the nation. By 2015, more than half of survey respondents saw immigrants as strengthening the country, while the share that saw them as a burden had fallen to 41 percent.

Significantly, the changes in attitudes toward immigrants coincide directly with Americans’ exposure to them. As of 2015, three-quarters of U.S. adults surveyed by Pew reported the presence of immigrants in their local communities, and the PRRI research organization has found that the more social contact native-born Americans have with immigrants, the more positively they see them. So it was with the Germans, the Irish, the Italians and the Jews. And so it will be with the Muslims, the Asians and the Africans. In the end, diversity promotes tolerance, not conflict.

Many recent immigrants have little experience with multiculturalism and learn to appreciate it only in America, where it has become so common. A 2013 study by the Anti-Defamation League found that while 36 percent of Hispanic Americans born outside the country harbored anti-Semitic views, the number dropped to 14 percent among Hispanics raised in the United States.

Those concerned about the future of American civilization, like Rep. King, should be reassured.