The street fight over “racism” between Rep. Elijah Cummings of Baltimore and President Trump reminds us that all political traumas eventually fade from memory to become an abstraction.

Last weekend, when Rep. Carolyn Maloney of New York proposed a Canyon of Heroes parade honoring 9/11 first responders, it struck me as grandstanding. Then the thought occurred: Why not? That awful day was 18 years ago, and it’s already drifting into the fog of history. Some people visit Civil War battlefields or World War I cemeteries in France...