MCALLEN, Texas — Every afternoon, dozens of immigrant families released by the U.S. government walk three blocks from the Greyhound bus station in this South Texas border city to a migrant shelter run by Catholic Charities. Along with the clothes slung over their shoulders, the migrants sometimes carry government-issued containers — dark-blue receptacles resembling lunch boxes, with plastic handles that shine in the mid-afternoon sun. On the front of each container, the black-and-white logo of the GEO Group, the for-profit prison corporation that operates immigrant detention centers in the United States, hints at the contents: power cords required to charge the electronic tracking bracelets that tens of thousands of migrant adults, including most of the asylum-seekers who come through McAllen, are required to wear around their ankles so that U.S.