The US once had an enviable reputation for welcoming academics and attracting some of the best brains on earth. But it is becoming increasingly clear that this era is coming to an end. A wall is being built around the US to repel terrorists and to prevent a repetition of the horrors of September 11 2001 - and many members of the global academic community have been caught on the wrong side of it.
Scholars from a host of nations, from the Middle East to Russia and China, are being effectively barred from entering, their applications for entry visas denied or delayed for months. Postgraduates are being prevented from taking up courses at US universities, while those already studying there are being put through the mill.
International conferences are being switched to venues outside the US to ensure that delegates can attend. Multinational collaborations are being tested to the limit as whole groups of scientists find themselves unable to work with their American colleagues. And some foreign nationals already resident in the US find they cannot attend meetings abroad or even visit their families for fear they will be unable to get back home.
The UK could benefit from a reverse brain drain, picking up many talented students and academics put off from studying across the Atlantic. But this would be scant comfort. If the US, with all its resources and tradition of excellence, becomes isolated from the rest of the world, all academe will be the poorer for it.