Progressives have welcomed migrants. Now they need to house them.

I’ll let you in on a dirty secret about journalism: Most of what we write — good, bad, or otherwise — is as evanescent as yesterday’s rain. Readers may get most of their news in digital form rather than paper these days, but the old adage still holds true: Today’s news is tomorrow’s fish wrap.

Every once in a while, though, writers on deadline produce something of lasting value, an insight that illuminates not just today, but the past and the future both, something that helps explain why we are where...