What does it mean if Mark Zuckerberg doesn’t obsess about you anymore?

Fortune’s story from last week on Twitter’s prospects contained some food for thought on the precarious existence of a social-media juggernaut.

Once mighty, now…leveling off?

Just two years ago Twitter was the hottest thing on the web. But in the past year U.S. traffic at Twitter.com, the site users visit to read and broadcast 140-character messages, has leveled off. Nearly half the people who have Twitter accounts are no longer active on the network, according to an ExactTarget report from January 2011. It has been months — an eternity in Silicon Valley — since the company rolled out a new product that excited consumers. Facebook’s Mark Zuckerberg used to watch developments at Twitter obsessively; now he pays much less attention to the rival service. Meanwhile companies are hungry to advertise, but Twitter hasn’t been able to provide marketers with enough opportunities. Last year the company pulled in a mere $45 million in ad revenue, according to research firm eMarketer. Facebook brought in $1.86 billion.

None of this will be news to tech followers, but “Trouble@Twitter” fits nicely in the journalistic traditions of Fortune, which invented the time-honored format we now know as the corporate profile, what it called “corporation stories,” back in the 1930s under Henry Luce. These are deep dives written for a general audience, invariably focused on past managerial and financial performance and future prospects. And this one is balanced, with some good inside skinny. The bottom line is that no one is writing off Twitter. But its future is far from the gimme it might appear to be.

The story documents the toll, for instance, taken by leadership turnover. The company, started in 2006 by the triumvirate of Jack Dorsey, Biz Stone, and Evan Williams, was first run by Dorsey until 2008, when Williams took over. Last fall, Williams announced he was stepping down, and COO Dick Costolo became CEO; and last month Dorsey came back as executive chairman. Got that? (Felix covered the amount of money Twitter was willing to throw at a Google executives before Dorsey came back.) And Fortune writer Jesse Hempel highlights tensions between founders Williams and Dorsey:

Williams, who succeeded him, has been accused of pushing Dorsey out, but in an exclusive interview for this story, he put the responsibility for making that decision on the broader board: “We thought about recruiting somebody from the outside,” he says, “but the company at that stage was so fragile that bringing in someone from outside was risky. So the VCs asked me if I would do it.”

By that time, communication among the Twitter founders, especially Dorsey and Williams, had started to fray. According to Greg Kidd, an early investor, Dorsey today is circumspect but firm on the subject of his relationship with Williams. “The most he’s ever said about Ev is, ‘We don’t talk.’

Vanity Fair has more on the Dorsey/Williams tensions and also on the idealism, expressed here by Dorsey, that seems to lie at the heart of Twitter’s culture.

“My role as an observer and as a technologist,” he says as he strides through a San Francisco rainstorm, holding a big blue umbrella, “is to show everything that’s happening in the world in real time and get us to that data immediately, so we can change our lives even faster, with better knowledge.”

One result: attempts to commercialize the site have been tentative.

And mostly the story points to a more fundamental problem: Twitter isn’t sure what it is yet.

Twitter CEO Costolo insists that the company isn’t a “social network.” But what is it? A media company? A communications tool? Or even something more? Twitter executives need to answer those questions, and fast.

It’s actually inspiring in some ways that something that started almost by accident became such a global force. And the fact that it hasn’t figured out—or really tried—to maximize its profit-making potential is not necessarily a bad thing for its users or its future as information exchange (or whatever it is).

But it’s disorienting to think that a global communications nexus one day is MySpace the next. As Reid Hoffman, co-founder of LinkedIn, says in the piece, “…it’s not a given. It’s never a given.”

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Dean Starkman Dean Starkman runs The Audit, CJR's business section, and is the author of The Watchdog That Didn't Bark: The Financial Crisis and the Disappearance of Investigative Journalism (Columbia University Press, January 2014). Follow Dean on Twitter: @deanstarkman.