This Christmas message was a foul warning of what we have become

On Christmas of all days, Donald Trump chose to call Democrats “scum.” Not criminals. Not misguided. Not wrong. Scum. A word we usually reserve for things we scrape off the bottom of a shoe or skim off polluted water. A word whose entire purpose is to dehumanize.

That moment matters far beyond the day’s news cycle, and far beyond partisan politics. It matters because leaders don’t just govern; they model.

Psychologists and social and political scientists have long pointed out that national leaders function...