Perhaps the most influential media document of the last four years is a chart by a co-director of the Berkman Klein Center for Internet and Society at Harvard, Yochai Benkler. The study showed that a dense new right-wing media sphere had emerged — and that the mainstream news “revolved around the agenda that the right-wing media sphere set.”

Mr. Bannon had known this, too. He described his strategy as “anchor left, pivot right,” and even as he ran Breitbart News, he worked to place attacks on Hillary Clinton in mainstream outlets. The validating power of those outlets was clear when The New York Times and Washington Post were given early access in the spring of 2015 to the book “Clinton Cash,” an investigation of the Clinton family’s blurring of business, philanthropic and political interests by the writer Peter Schweizer.

Mr. Schweizer is still around this cycle. But you won’t find his work in mainstream outlets. He’s over on Breitbart, with a couple of Hunter Biden stories this month.

And the fact that Mr. Bobulinski emerged not in the pages of the widely respected Journal but in a statement to Breitbart was essentially Mr. Bannon’s nightmare, and Mr. Benkler’s fondest wish. And a broad array of mainstream outlets, unpersuaded that Hunter Biden’s doings tie directly to the former vice president, have largely kept the story off their front pages, and confined to skeptical explanations of what Mr. Trump and his allies are claiming about his opponent.