Images of screaming children torn away from parents, photos of toddlers and even babies sitting alone in characterless detention centers, repellent bloviators defending the new policy as if splitting up families were itself the goal . . . the controversy over the Trump administration’s new “zero tolerance” policy on illegal immigration has turned into one of the great political debacles of our time.

The challenge isn’t new. Current law on detaining illegal immigrants has made border security nearly impossible. The problem arises most acutely when detained adults seeking asylum or some other legal status are accompanied by children. A 1997 Justice Department settlement, since reinforced by a 2016 appeals court decision, requires that the children of these detainees be kept in custody for no more than 20 days. That means immigration authorities must release parents and children together. They are supposed to return for their hearings but often do not, and so they remain inside the country as undocumented aliens. Hence when children are present, border enforcement officials are powerless to deter illegal crossings—bound to the policy of “catch and release.”