President Trump will make America smaller.

He may not be thinking in these terms. But as he barrels ahead with his promise to restrict immigration — barring people from some Muslim-majority countries, limiting work visas, expelling millions who are here illegally — the president might want to ponder how this fits the theme of making America “great again.”

For his plan, at the scale he promises, would shrink the American economy and impoverish the world. If greatness is what he pursues, a straightforward way to bulk up the economy — not to say bolster global growth — would be to allow many more immigrants in.

Consider the report on immigration released last fall by the National Academies of Sciences, Engineering and Medicine. It concluded that immigration to the United States from 1990 to 2010, both legal and illegal, produced net benefits worth $50 billion a year to the native population.

This might seem insignificant in an $18 trillion economy. But it packs more than meets the eye. It is more than the government’s estimate of what the country would have gained from the Trans-Pacific Partnership, the grand deal with 11 other countries around the Pacific Rim negotiated over eight years by the Obama administration but abandoned by Mr. Trump.