CNN  —  Ranjani Srinivasan was busy talking to an adviser at Columbia University when the federal agents first came to her door. The day before she’d got an unexpected email that her student visa had been canceled , and she was trying to get information. “It was my roommate who heard the knock and immediately recognized (it as) law enforcement,” Srinivasan told CNN. “She asked them ‘Do you have a warrant?’ And they had to say ‘No.’” “I was stunned and scared,” she said. “I remember telling the