It was Donald J. Trump at his neediest, pleading with the television anchor in front of him to acknowledge a poll that, he said, showed that Hispanics really do love him. “You saw that, right?” he asked. “Did you see it? Wait. Did you see it?”

It was Donald Trump at his wiliest, declaring in one breath that he had “no idea” who the anchor was and, in the next, reminding the journalist, Jorge Ramos, that he was the subject of a Trump lawsuit.

And it was Donald Trump at his most self-conscious, kicking Mr. Ramos out of a news conference and then, sensing that the mood in the room was turning against him, inviting Mr. Ramos back to pepper the candidate with questions. “Now I like him,” Mr. Trump told a press corps seemingly dazed from the whiplash.

The 30-minute news conference Mr. Trump presided over in Iowa on Tuesday night was the purest distillation of the psychological quirks and emotional idiosyncrasies that have made his candidacy such an irresistible spectacle — at times repellent, but often riveting.