NEW YORK (AP) — Less than three weeks after his release from an immigration jail, the Palestinian activist Mohsen Mahdawi strode across the graduation stage at Columbia University on Monday morning, savoring a moment the Trump administration had fought to make impossible. Draped in a keffiyeh, Mahdawi, 34, paused to listen to the swell of cheers from his fellow graduates. Then he joined a vigil just outside Columbia’s gates, raising a photograph of his classmate Mahmoud Khalil, who remains in federal custody.