There is a direct line from those who attacked the Trump administration for “family separation” at the border to the current pain and suffering of thousands of migrant children. Now that the Biden administration has carried out a policy these critics argued for, the result is a humanitarian disaster, and those who were most vocal about the care of migrant children are now silent.First, the backstory. A legal ruling says the federal government can’t detain migrant children in the United States for more than 20 days. If adults bring children with them to the southern U.S. border, assuming these children...