For a nation to be known for its outstanding universities it has to attract students from around the world. If it pulls this off, there’s another potential win: the country gains international friends and advocates for years to come. I learnt this as an exchange student at Berlin’s Humboldt university. Not only did I improve my patchy German but I made long-lasting friendships with fellow international students and discovered new ways of learning and expressing ideas in a system that was totally different to what I had experienced growing up in the UK.It’s crucial that universities foster these cultural exchanges. Unfortunately, this is a point on which Donald Trump differs. On Monday the US Department of Homeland Security issued a ruling prohibiting international students from returning to, or remaining in, the US if the colleges they attend adopt online-only models as part of measures taken in reaction to the coronavirus pandemic.For those currently studying in the US, the blow – even if temporary – is devastating. “I won’t have access to any of the resources I need to work towards my PhD,” I was told by a UK-born friend, Kate Birkbeck, who returned to England when the virus hit the US. “I can’t even take a break from the PhD because it would further jeopardise my precarious visa status. So I have to perform at the same high level, in a different time zone, with no resources. This is part of a long-term push to make all sorts of immigration statuses untenable and it is very likely that that will put an end to my life in the US and in academia.”This pandemic has repeatedly seen Trump launch opportunistic attacks on his country’s immigrant population, including restricting work visas and limiting asylum claims. This latest decision will be felt not only by students but also by the institutions they attend. The US might be home to some of the world’s leading universities, but it’s their ability to draw in academic talent from around the world that keeps them at the top of their game.