Perhaps Barack Obama can likewise reassert himself in Tuesday evening's town hall in Long Island. But his problem is this: 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.

Mostly this image was the making of his own immodesty, starting the night he clinched the 2008 Democratic nomination. Mr. Obama might have simply declared victory and congratulated Hillary Clinton on a valiant fight. Instead it became the backdrop for one of his more infamous egoisms. History, he said, would look back at his victory as the moment "the rise of the oceans began to slow and our planet began to heal."

This was no aberration. A man who interviewed for a job on the campaign was told by Mr. Obama: "I think that I'm a better speechwriter than my speechwriters. I know more about policies on any particular issue than my policy directors. And I'll tell you right now that I'm gonna think I'm a better political director than my political director."

Everything about his campaign fed that idea. The Styrofoam Greek columns at the Democratic convention when he was nominated. The faux presidential seal with its own Latin motto. And before the campaign, the two books he authored about—himself.