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.

Columbia University says it has expelled or suspended some students who took over a campus building during pro-Palestinian protests last spring and temporarily revoked the diplomas of some students who have since graduated.