Last week, just two short days before Donald Trump tested positive for the coronavirus, several of my colleagues wrote a story about the early days of the pandemic, and the strong global public health consensus at the time that open borders and free movement of peoples should not be suspended, even in the face of a swiftly spreading virus.

“The policy of unobstructed travel was never based on hard science,” the story notes. “It was a political decision, recast as health advice” that for a public-health community committed to cosmopolitan ideals had become “an article of faith”.