“If you’re … pathetically weak, the country is going to be overrun with millions of people, and if you’re strong, then you don’t have any heart, that’s a tough dilemma. … I’d rather be strong.” So said President Donald Trump, on issuing his order halting the separation of children from parents caught breaking into the country. Trump’s enemies are celebrating a victory. Yet the issue remains. Under U.S. law, teenagers and tots cannot be detained for more than 20 days and must be held in the least-restrictive facilities. But if the children cannot be separated from the parents as they...