Khalil’s arrest could have a chilling effect on on- and off-campus protests involving people who aren’t citizens, said Columbia University immigration law professor Elora Mukherjee. Already, she said, it had provoked panic and fear among immigrant students on campus.

The Trump administration’s apparent attempt to deport pro-Palestinian activist Mahmoud Khalil could be one of the most important free speech cases in recent American history. If only we knew precisely what it was about.