To be sure, it’s been almost six weeks since Trump has led Mrs. Clinton in any nationwide poll, and the RCP average has her up 6.2 points. Absent evidence of systematic polling bias in her favor, Mrs. Clinton would have to be reckoned the favorite. Even Scott Adams admitted as much yesterday, opining on his blog that “[Mrs.] Clinton’s side”—as distinct from her campaign—“is totally winning the persuasion battle” because it has “been viciously effective at branding Trump a crazy racist.”

Adams thinks Trump can rebrand himself, and expects him to do so. We’ll see. But the analysis suggests another important point: Unthinkability bias could end up working in Mrs. Clinton’s favor. Most of the pundits for whom a Trump presidency is unthinkable also oppose a Trump presidency, whether they favor Mrs. Clinton or not. Indeed, “he can’t possibly beat her” is a standard argument for Nevertrump conservatives.

If Mrs. Clinton’s side can convince enough wavering voters that a Trump presidency is unthinkable—because he’s a “crazy racist” or whatever—she could win the election more or less by default. Even her campaign seems to be thinking in these terms.