As construction of the border wall continues, so does the flow of undocumented migrants hoping for a better life. On the night of Halloween in 1999, Carmen Caballero, who was then eight, and her three-year-old sister put on witches’ costumes and met their aunt for a trick-or-treat excursion in their native city of Juarez, Mexico. They piled into their aunt’s car and left. When the girls got out, they were in El Paso, Texas.