He deemed BuzzFeed News “a failing pile of garbage,” mocked an inquiry about his tax returns — “Gee, I’ve never heard that one before” — and, in an unheard-of moment for a presidential news conference, shouted down questions from a CNN reporter, declaring, with some menace, “Not you.”

“Your organization is terrible,” said President-elect Donald J. Trump, his voice rising as Jim Acosta of CNN tried to interject. “No, I’m not going to give you a question. I’m not going to give you a question.”

“You,” the president-elect said, as Mr. Acosta and other stunned journalists looked on, “are fake news.”

Any hope that Mr. Trump would temper his attacks on the news media after the campaign seemed to dissipate in the marble atrium of Trump Tower on Wednesday, as the president-elect, holding his first news conference since July, turned a controversy over his ties to Russia into a deft and unrelenting attack on the journalists who reported it.