The system is geared towards keeping out a tiny number of terrorists. Fair enough—such people should indeed be kept out. But there should be a trade-off. An immigration official lives in fear of admitting the next Mohammed Atta, but there is no penalty for excluding the next Einstein, or for humiliating tourists who subsequently summer in France. Osama bin Laden has arguably inflicted more harm on America indirectly than directly. To stop his acolytes from striking again, the government has made entering America far more difficult and degrading than it need be.

This has slowed the influx of foreign brains. In 2001, 28% of students who studied abroad did so at American universities. By 2008 that figure had shrunk to 21%, though since the absolute number of globally mobile students grew by 50% over that period, the absolute number in America has flattened, not fallen. Does this matter? Well, foreigners and immigrants make up more than half of the scientific researchers in the United States, notes Edward Alden, the author of a fine book called “The Closing of the American Border”. Among postdoctoral students doing top-level research, 60% are foreign-born. Boffins flock to America because its universities are the best, but the ordeal of getting a visa prompts many to take their ideas elsewhere.

A similar problem afflicts even short-term visitors. Organisers of international scientific conferences are increasingly reluctant to hold them in America because not everyone they invite will be able to attend. Last year, for example, Alik Ismail-Zadeh, a prominent Russian geophysicist, applied for a visa to attend a meeting of the American Geophysical Union. He allowed three months, but did not get his passport back until after his plane had departed. Kathie Bailey-Mathae of the National Academy of Sciences says that the hassles have eased in the past year, but only somewhat. When foreign scientists run into problems repeatedly, they become loth to collaborate with their American peers, she says.

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