Like most of the founding generation, Crèvecœur believed the sheer size of the new nation meant for a prosperous future. But he was also celebrating an attitude of openness, a willingness to embrace new citizens from around the world into what he called the “melting pot” of American society.

The embrace of openness has survived, in spite of occasional outbreaks of anti-immigrant sentiment, for the intervening two and a half centuries. The United States remains an immigrant nation, in spirit as well as in fact. (A fact for which, as an immigrant from the Old Country, I am grateful). My wife is American, and my high schoolers have had U.S. passports since being born in London. Right now I’m applying for U.S. citizenship. I want America to be my home, not just my residence. My story is of course very different to most immigrants – but the point is, all of our stories are different. What unites us is our desire to be American.

But this spirit may be waning. Thanks only in part to Donald Trump, immigration is near the top of the political agenda – and not in a good way.

Trump has brilliantly exploited the imagery of The Wall to tap into the frustrations of white middle America. But America needs immigration. At the most banal level, this is a question of math. We need more young workers to fund the old age of the Baby Boomers. Overall, immigrants are good for the economy, as a recent summary of research from Brookings’ Hamilton Project shows.

Of course, while immigration might be good for the economy as a whole, that does not mean it is good for everyone. Competition for wages and jobs will impact negatively on some existing residents, who may be more economically vulnerable in the first place. Policymakers keen to promote the benefits of immigration should also be attentive to its costs.

But the value of immigration cannot be reduced to an actuarial table or spreadsheet. Immigrants do not simply make America better off. They make America better. Immigrants provide a shot in the nation’s arm.

Immigrants are now twice as likely to start a new business as native-born Americans. While rates of entrepreneurialism are declining among natives, they are rising among immigrants. Immigrant children typically show extraordinary upward mobility, in terms of income, occupation and education. Among children born in Los Angeles to poorly-educated Chinese immigrants, for example, an astonishing 70% complete a four-year-college degree.

As the work of my Brookings colleague William Frey shows, immigrants are migrants within the U. S., too, moving on from traditional immigrant cities — New York and Los Angeles — to other towns and cities in search of a better future.

New Americans are true Americans. We need more of them. But Trump is tapping directly and dangerously into white fears of an America growing steadily browner. According to a 2011 Pew Research Center survey, more than four in ten white seniors say that a growing population of immigrants is a “change for the worse;” half of white boomers believe immigration is “a threat to traditional American customs and values.”

Immigration gets at a deep question of American identity in the 21^st century. Just like people, societies age. They might also settle down, lose some dynamism. They might trade a little less openness for a little more security. In other words, they get a bit stuck in their ways. Immigrants generate dynamism and aspiration, but they are also unsettling and challenging.

Where this debate ends will therefore tell us a great deal about the trajectory of the nation. An America that closes its doors will be an America that has chosen to settle down rather than grow, allowing security to eclipse dynamism.

Disruption is not costless. But America has always weighed the benefits of dynamism and diversity more heavily. Immigration is an important way in which America hits the refresh button and renews herself. Without immigration, the nation would not only be worse off, but would cease, in some elemental sense, to be America at all.

Richard V. Reeves is a Senior Fellow in Economic Studies at the Brookings Institution.