The US Congress is again debating how to permanently welcome Dreamers, the hundreds of thousands of undocumented immigrants who came to the US as children.

A core question for lawmakers will be whether that means significantly downsizing the ideal of America as a country of immigrants: In exchange for letting Dreamers stay, Donald Trump is demanding an end to “chain migration,” the family reunification policy that, by the president’s own definition, describes how millions of immigrants became Americans.

But that kind of anti-immigrant push is nothing new. In the early 1900s, a backlash against immigrants led to stiff restrictions in 1924. By 1965, Americans were up on immigration again, and the restrictions were replaced with a more open immigration system. US politicians have gone back-and-forth on immigration many times since—even as immigrants have kept coming.

If Donald Trump succeeds in passing his nativist agenda, history suggests Americans will eventually reverse it. As studies in psychology, sociology and political science show, immigration is deeply imprinted on US culture, from the way Americans smile to the environments that make them feel most at home.

The way Americans smile

Trump has spotlighted—and emboldened—a sector of American society that feels threatened by immigrants. White Americans, in particular, are anxious about becoming a minority, and are therefore feeling less fond of diversity, research shows.

But there are multiple reasons to believe those are not the attitudes that will prevail. Immigration has defined the US and its citizens from the very start—down to how often and why they smile.

Smiling, and showing emotions in general, is more common in countries that are historically diverse than in homogenous places, say researchers from Niedenthal Emotions Lab, at the University of Wisconsin, Madison. Individuals in diverse societies have to rely on emotional expression to navigate the panoply of foreign cultures, social norms, and languages they came across during the course of everyday life.

Among nine countries studied by the researchers, the US had the highest share of people who see smiles as a way to be friendly or bond with others—more than 80%. In more homogenous countries, such as Japan, people are less likely than Americans to crack a smile to show friendliness, and more likely to do it to assert their superiority.

The way Americans think

Immigration is also embedded into Americans’ psychology. “All Americans, that is, all non-Indian Americans, have left an old world behind,” wrote the late Bruce Mazlish, a Massachusetts Institute of Technology professor known for applying the lens of psychoanalysis to history. That separation, along with the tensions and contradictions it generated, shaped who they became in their new world, he continued in a 1990 book of essays.

Here’s how Mazlish describes those early drivers of the American way:

The need to return to the ideal and reverse a declension; the need to experience a rebirth; the need for sons to stand free of their parents, especially fathers; and the need to repudiate the traditions and values of the old civilization of Europe. From being an English colonist now emerges an American.”

Some of them are still tangible today, for example, in Americans’ spirit of independence and individuality. The notion of a new beginning still shapes how Americans—and foreigners—see the US. It’s visible in enduring ideals such as the American dream or in the real rags-to-riches stories of foreign entrepreneurs.

The way Americans hear

Immigrants to the US—and their descendants—don’t have the millenary myths or ethnic homogeneity that binds the citizens of their countries of origin. What they have in common is the immigrant experience, and the civic values enshrined in the Constitution. That’s why the melting pot concept continues to have currency, even among immigration hawks, who say it’s not immigration that’s the problem, but illegal immigration.

“Even people quite opposed to increased immigration nonetheless go out of their way to make it very clear they are very staunch backers of legal immigration,” says Daniel Hopkins, a political scientist at University of Pennsylvania who researches attitudes towards immigrants. (Ultra immigration hardliner and Republican politician Tom Tancredo, for example, launched his presidential bid in 2007 on the premise that “the great tradition of the melting pot in America” was not working due to illegal immigration.)

Hopkins’s studies also suggest that Americans are less hostile to immigrants who demonstrate their willingness to “melt” into the proverbial pot. In fact, in one of his experiments, subjects who watched clips of immigrants speaking with varying degrees of English fluency were more supportive of the ones with broken accents.

“The native-born Americans hear that effort and think of that immigrant in the tradition of generations and generations of immigrants coming to the US and seeking a better life,” he says.

The American welcome

American attitudes on immigration are not solely rooted on the longstanding ideal of the US as the land of opportunity. They are also in large part based on everyday interactions with today’s immigrants. And research suggests that when Americans live with immigrants, they warm up to them.“The immigrants’ experience gets woven into the lives of the entire region,” says Stanford professor Tomás Jiménez.

A recent study he co-authored gives an idea to what extent. It sought to determine the impact of local policies designed to welcome immigrants—or repel them—on the broader community. Jiménez and his colleagues asked white and Latino residents in New Mexico and Arizona to randomly consider two sets of policies, one welcoming to immigrants, the other hostile. They then tallied how the two sets of policies made participants feel—angry, happy, or sad—and whether they left them feeling at home in their state or wanting to move elsewhere.

It’s no surprise that the welcoming policies elicited positive feelings among immigrants and gave them a greater sense of belonging. But those policies also had a positive effect on people who were born in the US—with the exception of white conservatives. (Hostile measures made white conservatives feel more positive, and at home.) This is what the researchers concluded:

These findings suggest that debates about the polarizing effects of immigration policies by racial group are misplaced. With a majority of whites nationally identifying as either liberal or moderate, welcoming immigration policies have direct and spillover effects that can further national unity.

In other words, a community that welcomes immigrants makes most non-immigrants feel more welcome, too.