A fine tradition in the United States is the annual visit of the current American Nobel laureates to meet the US president in the Oval Office ¨C an event that takes place between the announcements in October and the ceremonies in Stockholm in December.

In 2015, I was one of four Americans to be so honoured. Three of us were immigrants, the fourth the son of an immigrant ¨C facts that were not lost on President Obama. One of us, Aziz Sancar, whose work on DNA repair might one day lead to a cure for cancer, was born of illiterate parents in Turkey, a Muslim-majority country. Another, William Campbell, who among other achievements discovered the cure for river blindness, was born in Ireland, a country that might well be labelled as ¡°terror-prone¡±.??

Neither Ireland nor Turkey was included in President Trump¡¯s recent executive orders banning refugees and immigrants, but they might well have been. Along with nearly 15,000 other academics, and 50 Nobel laureates, I signed a protesting these orders. They are foolish, arbitrary, counter-productive, and likely illegal, at least in part. Their singling out of one religion is un-American and may be unconstitutional. News reports claim that they were drafted by Trump¡¯s immediate cronies, without vetting or assessment by government agencies.?

Members of ISIS are not applying for visas from the Middle East. The students and faculty whose lives and families are being disrupted by these measures are as opposed to terrorism as we are. These orders hurt our friends, not our enemies, and undermine America¡¯s influence abroad, as well as our scientific advance at home.

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Listen again: THE books editor Karen Shook talks to Sir Angus

America risks retreating into an isolationist pre-Enlightenment stance, in which policy is rooted in fear, not reason, a stance that characterises our enemies, not our friends.?

One of the tasks that academics are paid for is to show that first thoughts are not always the best thoughts, or even good thoughts, and to expose and counter populist fallacies about trade, immigration, refugees, religion and terrorism. But experts have fallen deeply out of favour, in part through their own hubris.?

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In my own subject of economics, more than two-thirds of new PhDs were born outside the United States. The department from which I recently retired, Princeton, fits the pattern, with more than 20 different countries of birth and all five continents represented. We are decidedly short of women, another important source of diversity in thought, but one of the four we have is a talented young Iranian.

The influx of refugees into American academia from Europe before and during the Second World War is well known, as are its effects on American science, with the Manhattan Project a famous example. The current wave of immigrants is less well-studied, but its effects have also been profound, at least in economics. Young people bring their own cultures, their political beliefs, and their passions with them, and American economics has become immeasurably better, more interesting, and more diverse, as a result.

In economics, as in other areas, return migrants have been beneficial to the world. China and India are two of the countries in the world whose growth and development have been immeasurably enhanced by the return of citizens who learned and worked in the US. Isolationism and fear can slow poverty reduction and the growth not only of the US but of the rest of the world.?

Yet the great American universities are not blameless. They have long been dangerously isolated from the society in which they are located and which ultimately supports them.

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Many academics live in liberal, cosmopolitan bubbles, little penetrated by rumblings from outside the walls. Elite universities run the risk of serving, or being seen to serve, only the very rich, minorities, and foreigners, leaving little access for the American working class. Those with relatively little education have shared little in the rising prosperity of the coasts, their health and life expectancy are faltering, and they have steadily lost political influence ¨C at least until they elected Trump.?

Beyond academia, the deepest concern is whether the American constitution will survive Trump. The famous checks and balances are not always quick to come into play, although the courts are trying. Republican congressmen who oppose Trump are hamstrung by a primary system that imposes a preliminary hurdle where the voters are Republican stalwarts who favour Trump by large majorities.

The founders were deeply concerned about whether a republic could withstand a populist assault, and I am afraid that we are about to find out whether the constitution that they designed is up to the task.

Angus S. Deaton is senior scholar and the Dwight D. Eisenhower professor of economics and international affairs emeritus at the Woodrow Wilson School of Public and International Affairs and the economics department at Princeton University.?In 2015, he was awarded the Nobel Prize for Economic Sciences.

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