The first headlines from Michael Wolff's book "Fire and Fury: Inside the Trump White House" were about Steve Bannon's shocking quotes. With the Bannon v. Trump feud dominating the news cycle, some of Trump's aides and media allies dismissed the stories as "gossipy" and "tabloid."

White House Press Secretary Sarah Sanders used both words at her briefing on Thursday, saying the book was "full of tabloid gossip."

"It's just a salacious book. It's so tabloid," "Fox & Friends" co-host Ainsley Earhardt said Thursday. She asked viewers: "Do you really care?"

Yes, many people do care. Pre-orders of the book have sent the book soaring to No. 1 on Amazon's best sellers list. It's now coming out on Friday, four days earlier than planned.

But the coverage of the "salacious" details misses the bigger, more important point of Wolff's reporting.

The excerpts published so far leave little doubt: The book suggests that President Trump is unstable and raises alarms about his fitness for office.

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Wolff had enviable access to the West Wing during Trump's first months in office. He spoke with many top officials like Bannon and lower-level aides. He wrote in The Hollywood Reporter on Thursday that "my indelible impression of talking to them and observing them" is that "they all — 100 percent — came to believe he was incapable of functioning in his job."

The president, incapable of being president. It is a disturbing thought.

And it's a lot more important than, say, the passages in the book about Trump's penchant for cheeseburgers.

Between Wednesday and Thursday, there was a noticeable shift in the news coverage of "Fire and Fury," away from the specific and sometimes gossipy claims and toward the bigger-picture portrait of a White House in crisis.

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The excerpts portray the president as erratic; easily distracted; uninterested and unsure about the basics of his job.

Wolff's sourcing and methods have already come under scrutiny, but much of what he's writing is just affirming what other journalists have already reported. This has been a theme of some of the cable news coverage.

Wolff's accounts are "pretty consistent" with past reporting, Bannon biographer Joshua Green noted on CNN Thursday afternoon.

Concerns about Trump's fitness were already in the news bloodstream because of his jaw-dropping tweets on Tuesday about jailing political opponents and controlling a "nuclear button."

"Should Americans be concerned about the President's mental fitness," NBC's Peter Alexander asked in Wednesday's press briefing, given that "he appears to be speaking so lightly about threats regarding a nuclear button?"

On CNN's "Erin Burnett OutFront" Wednesday night, former presidential adviser and CNN senior political analyst David Gergen said Wolff's reporting reinforce questions about whether Trump is fit for office.

"I do think we need to have a serious national discussion about this," Gergen said. And "by the way," he added, "I think the Republican party bears some responsibility here."

The subject came up at the White House briefing again on Thursday.

Sanders was asked: "What's the president's reaction to the growing number of suggestions, both in this book and in the media, that he's mentally unfit to serve as president?"

She called those suggestions "disgraceful and laughable."

On Wednesday, Trump questioned Bannon's mental acuity by saying his former aide had "lost his mind."

Some commentators raised doubts about Trump's competency even before Election Day. But there's been a palpable change as of late. Media conversations about Trump's competency are certainly more common than, say, six months ago.

Jake Tapper said on CNN's "The Lead" on Thursday that "this new book and the new tweet about his big and powerful button" are "renewing talk about the 25th Amendment and lawmakers' fears about President Trump's mental health." He asked: "Is this all below board?"

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White House aides and pro-Trump hosts on Fox News say that it is completely inappropriate to be questioning his stability.

But Republican Senator Bob Corker has broached the subject several times in recent months. Last October he called the White House "an adult day care center."

On Thursday it was reported that a Yale psychiatrist briefed a dozen members of Congress -- mainly Democrats -- last month on Trump's mental fitness.

The meeting was kept private at the time. These questions about fitness are more frequently whispered than shouted.

On MSNBC on Thursday, anchor Katy Tur, who covered the Trump campaign, recalled that a former Trump staffer asked her a couple of months ago, "Do you think he's lost a step since the campaign?"

"This," she said, "is a pervasive view among those who know him. That should not be surprising."

But it is surprising -- and disturbing -- to many viewers and readers. Books like "Fire and Fury" are bringing these fears to the forefront.