A Diagnosis for American Polarization

Why are evidence and reason largely absent from political discussion? Why are well-supported facts often no match for emotion? Much of it can be explained by a process called “splitting.” Though little known to the public, the term is used widely by mental-health professionals.

I first noticed splitting a few years ago, when I provided psychotherapy to a depressed college student. At first our sessions focused on her depression, but my patient, a white woman, took frequent detours into racial politics. She “loved” Malcolm X and railed against “white privilege.”...