NUEVO LAREDO, Mexico — Blanca Navidad is the name of a dusty squatter's quarters that doesn't have too much to cheer about. It is a barren plot of land where some of Nuevo Laredo's poorest residents live, literally, in oversize plywood boxes. There's no water and no electricity. This year, the mayor unsuccessfully tried to dislodge the residents of Blanca Navidad and force them to move to already-developed low-income areas. On Tuesday, Subcomandante Marcos, the near-mythical masked leader of the Zapatista National Liberation Army, rallied the neighborhood and used it to launch a tirade against politicians from here to Mexico...