President Trump is wrong on immigration. (Jeff Roberson/AP)

President Trump has spent months denigrating immigration and its impact on Americans as part of his call for greater restrictions on who can enter the country. Listening to him, one would think immigrants destroy American society.

Yet in reality, a major anniversary today reminds us that immigrants have long benefited the United States in many crucial areas. Dec. 2 is the 75th anniversary of the birth of the nuclear age, the creation of the world’s first nuclear chain reaction at the University of Chicago. This triumph of nuclear science was the first step in the development of America’s first atomic weapons. From the very start, immigrants were a vital part of this top-secret project, which was a pivotal step in securing the future of the free world.

First and foremost among these was an Italian immigrant named Enrico Fermi. Already a giant in physics when he arrived in the United States in January 1939, Fermi led the effort to create a nuclear chain reaction from its beginning at Columbia University. For much of this effort he was legally an enemy alien, a citizen of a country at war with the United States.

Initially he was a reluctant participant, understanding that, if successful, his work could lead to weapons of unprecedented destructiveness. But he soon realized that some of the world’s greatest physicists, such as Werner Heisenberg, would remain in Nazi Germany and work to develop atomic weapons for Hitler’s genocidal regime. If they had such weapons, the Germans would not hesitate to use them against cities such as London or even New York. The United States had to win the race to the bomb to save the world, and Fermi threw himself into the American project with energy and conviction.

Surely one of the most bizarre aspects of the project was the presence of an enemy alien at its very heart. Echoing the claims of some on the right today about the danger of immigrants from hostile nations, some wanted to deny Fermi a security clearance, conveniently overlooking the fact that much of what was secret about the project originated in his brain. Ultimately, The U.S. government wisely ignored the critics.

In return, Fermi was passionately loyal to his adopted country and made professional and personal sacrifices to play his central role. His family life suffered, and he may have even sacrificed his health — he died of stomach cancer in 1954 at the age of 53, perhaps as a result of his career-long work with radioactive materials. When he arrived on our shores, fleeing fascist Italy, he was probably the most knowledgeable man in the world on how neutrons interact with matter, an expertise that enabled him to create the first nuclear reactor in an astonishingly short period of time. His expertise was crucial in this development — German scientists never matched it.

Another immigrant integral to the development of the bomb was the eccentric Hungarian Leo Szilard. Szilard first had the idea of a nuclear chain reaction in 1933. In January 1939, Szilard collared Fermi at Columbia University when the news that German scientists had split the uranium atom crossed the Atlantic, pleading with Fermi to explore whether this uranium fission might create a chain reaction, thus enabling the development of nuclear weapons. Szilard, a friend of German émigré Albert Einstein, persuaded Einstein to sign a letter to President Roosevelt urging priority work on nuclear weapons.

Szilard worked alongside Fermi through December 1942 and was instrumental in key technical choices that enabled the most efficient chain reaction possible. Szilard, like Fermi, understood the dark side of the nuclear age, and while he congratulated Fermi on that fateful day in December 1942, he also said that it would go down as a black day in human history.

A childhood friend of Szilard’s in Budapest, Eugene Wigner was another key member of the team. A legendary quantum theorist, Wigner was key in persuading Fermi to brief the U.S. Navy on the potential of atomic weapons in March 1939. It was his bottle of Chianti with which the participants toasted the dawn of the nuclear age underneath the stands of the University of Chicago’s football stadium. The participants all signed this famous bottle after the event.

These immigrants and many others continued to play major roles throughout the Manhattan Project, working on every facet of the effort.

That we are a nation of immigrants is obvious, but the events leading up to the birth of the nuclear age give specific and profound meaning to this platitude. These talented men and women understood the unprecedented dangers inherent in the development of nuclear weapons, but they were also keenly aware that they were in a race against German scientists and a Nazi regime that would not hesitate to use these weapons against allied military and civilian targets. They had never ventured into the sphere of political or military affairs before, but in 1939 felt compelled to do so out of loyalty to their adopted country and a certain knowledge of what would happen if the Axis powers got hold of these weapons first.

Germany surrendered before either side succeeded in developing these weapons, and scientists have ever since been deeply involved in the public and private debates over U.S. nuclear weapons policy, beginning with the discussions about whether to use of the bomb against Japan in August 1945.

The decision to participate in the Manhattan Project was not easy for these brilliant immigrants. They understood the implications of what they were doing, but they were convinced that the potential costs of failure far outweighed the inherent dangers of actually succeeding. With the Soviet test of a nuclear weapon in 1949, it seems clear that they were right. Soviet unilateral possession of nuclear weapons would have altered the situation on the ground in Europe, and it would have been difficult to keep our allies in Western Europe from falling into the Soviet sphere of influence.

When we turn away immigrants today, are we sending away men and women who might develop the cure to cancer or other diseases? Whose minds will create new technologies that could radically transform the way we live? Who might offer new theories of how the universe works? Who could make our lives better in ways we can hardly imagine? Who might work to help protect and defend us from new and evolving threats, such as cyberwarfare?

The 75th anniversary of the nuclear age reminds us that immigrants have played a critical role in our national life before — and can be expected to do so as long as we welcome them.