As an Australian who wrote about the demonstrations while on campus, I gave my phone a superficial clean before flying to the U.S. I underestimated what I was up against.

Many people are detained at U.S. airports for reasons they find arbitrary and mysterious. I got lucky—when I was stopped by Customs and Border Protection last week, after flying to Los Angeles from Melbourne, a border agent told me, explicitly and proudly, why I’d been pulled out of the customs line. “Look, we both know why you are here,” the agent told me. He identified himself to me as Adam, though his colleagues referred to him as Officer Martinez. When I said that I didn’t, he looked surprised. “It’s because of what you wrote online about the protests at Columbia University,” he said.