Open this photo in gallery: Students protestors gather in protest inside their encampment on the Columbia University campus in New York on April 29.Stefan Jeremiah/The Associated Press Colleges around the U.S. implored pro-Palestinian student protesters to clear out tent encampments with rising levels of urgency Monday, including an ultimatum from Columbia University for students to sign a form and leave the encampment by the afternoon or face suspension. Columbia activists defied the 2 p.m. deadline with chants, clapping and drumming from the encampment of more than 300 people. No officials appeared to enter the encampment, with at least 120 tents...