President Donald Trump has used emergency powers during the coronavirus pandemic to implement the kind of strict enforcement regime at the U.S. southern border he has long wanted, suspending laws that protect minors and asylum seekers so that the U.S. government can immediately deport them or turn them away. Citing the threat of “mass, uncontrolled cross-border movement,” the president has shelved safeguards intended to protect trafficking victims and persecuted groups, implementing an expulsion order that sends migrants of all ages back to Mexico in an average of 96 minutes. U.S. Border Patrol agents do not perform medical checks when they...