The email did not mention that the article would also assert that Mr. Mueller had substantial evidence of the supposed presidential marching orders — a vital component that gave the story so much apparent heft.

To be fair, Fortress Mueller has been a frustration for reporters. The special counsel’s office has kept leaks to a minimum while refusing, for the most part, to confirm or deny whatever report about its work is firing up the news algorithm. While its impenetrability may explain the BuzzFeed reporters’ casual-seeming approach, it’s not much of an excuse for skipping the steps taught in Journalism 101.

The Mueller team’s challenge to the BuzzFeed report is also exposing the flaws of the wider media ecosystem, which is all too ready to spring into action at any sign of the Big One. Within minutes of the article’s publication on Thursday, Twitter was ablaze, and cable panelists were effusive. “This is stunning,” Don Lemon said on CNN. Lawrence O’Donnell spoke of “a Nixonian moment” on MSNBC.

Fox News reported the article’s claims as potentially an “enormous, enormous problem for this presidency.” But the guest who described it that way, the Fox News contributor Guy Benson, also warned, “Proceed with caution on this story — it may be true, it may not.”

By the following morning, other news organizations had failed to match the BuzzFeed piece with their own reporting and increasingly included “if true” caveats — but that didn’t prevent hours of on-air speculation about the potential implications of “subornation of perjury,” with its echoes of Watergate.

Even after the special counsel’s statement on Friday night, Rachel Maddow of MSNBC speculated that it wasn’t a true denial. During an interview with Mr. Smith, she asked, “Do you have any concern that this statement from the special counsel’s office might be an effort to dissuade you and dissuade your reporters from pursuing this, even if it is accurate, either because it interferes with the special counsel’s investigation in some way or it is otherwise too uncomfortable for this Justice Department?”