A prominent rabbi at Columbia University took the drastic step Sunday of warning Jewish students to go home and not return to campus because of “extreme antisemitism” at the Ivy League school. The dire directive followed yet another night of virulent anti-Israel protests on campus — which included one protester holding up a sign suggesting that students waving Israeli flags should be the next target of Hamas terrorists.” The events of the last few days, especially last night, have made it clear that Columbia University’s Public Safety and the NYPD cannot guarantee Jewish students’ safety in the face of extreme...