Nationwide protests are planned this weekend after Mahmoud Khalil, a former Columbia University student activist, was arrested by immigration authorities, fueling tensions between the Trump administration and student movements over immigration policy.

Between classes, when throngs of students stream into and out of Columbia University’s campus, the security lines can back up like a TSA checkpoint. There’s a switch-back path of metal fencing that leads into a white tent, where two sets of guards check and then swipe campus ID cards before letting students in and out.