Immigrant families fleeing civil strife must give up their privacy in new ways.   Under mounting political pressure from its northern neighbor, Mexico has been allowing agents of the United States deep into its territory to allow the bulk collection of biometric data, such as fingerprints and retinal scans, from Central American migrants fleeing domestic violence and civil conflict in their own homeland.   The questionable legality of any of this aside, Trump’s aggressive, nativist immigration policy is placing undue strain on a program that has made Mexico and the U.S. unlikely partners in the fight to stop the flow of undocumented labor across