By NICHOLAS FANDOS Rep. Nydia M. Velázquez (D-N.Y.) has a word of warning for Zohran Mamdani, the New York City mayor she just helped to elect: Back off city politics. Tension has quietly been growing between the two Democratic allies for weeks over who should succeed Velázquez in Congress as she retires after 32 years representing parts of Brooklyn and Queens. But Velázquez pushed it into the open Thursday in an interview with The New York Times, when she formally endorsed Antonio Reynoso,...