The latest furor over Trump immigration policy involves the separation of children from parents at the border. As usual, the outrage obscures more than it illuminates, so it’s worth walking through what’s happening here. For the longest time, illegal immigration was driven by single males from Mexico. Over the last decade, the flow has shifted to women, children, and family units from Central America. This poses challenges we haven’t confronted before and has made what once were relatively minor wrinkles in the law loom very large.