In Denver he didn’t just lose a debate—he lost the carefully cultivated illusion of a larger-than-life figure who was Lincoln and FDR and Moses all wrapped in one. …

Yes, we had earlier glimpses that Mr. Obama might not be all he has pretended. We saw how quickly he becomes irritated whenever an interviewer departs from the full fawn, such as when a Dallas TV reporter corrected him about his margin of defeat in Texas in the last presidential election. We’ve even seen the occasional lampoon, such as the 2008 Saturday Night Live skit satirizing how journalists who went hard on Hillary Clinton during Democratic debates served up softballs to Mr. Obama.

These, however, were only moments. They were nothing like the 90 minutes of presidential incoherence in Denver and the outrage of liberals who now hail Joe Biden for his savvy—not to mention the days of pointed, sustained Obama ridicule on late-night TV that, for the first time, laughed at the president rather than with him.