Anyone who pays the slightest attention to the daily passage of events in the news was aware that white-supremacist alt-right groups were planning a rally in Washington, D.C., this past weekend. The anticipatory media coverage of the event didn’t quite reach Super-Bowl hype levels, but it was close. And the number of white supremacists who showed up for the Sunday rally?

Not 200. Not 100. About 20.

This...