Earlier this afternoon, George Stephanopoulos and John McCain conducted an interview via Twitter. (Okay, fine: they conducted a Twitterview.) Some highlights (and I use that word loosely):

Stephanopoulous: @SenJohnMcCain AIG: Would a President McCain break bonus contracts? Obama teams says that would cause more harm than good

McCain: @GStephanopoulos i would have never bailed out AIG, the real scandal is billions to foreign banks.
Stephanopoulous: @SenJohnMcCain What worries you more: Pakistan or Iran?

McCain: @GStephanopoulos both. the challenges are different but both significant.

Stephanopoulous: @SenJohMcCain Cheney said on CNN that Obama putting US at risk of new terror attack Agree?

McCain: @GStephanopoulos too early to draw that conclusion.

Stephanopoulous: @SenJohnMcCain Lots of twitterers want to know: what do you think of Meghans’s feud with Coulter and Ingraham?

McCain: @GStephanopoulos I’m proud of my daughter and she has a right to her opinions.

On the one hand, I found the let’s-give-this-a-whirl attitude of experimentation at the core of the, er, Twitterview to be admirable. On the other, though, that same attitude—breezy, nonchalant—is, in the context of serious political reporting, pretty obnoxious. The substance of the dialogue itself—to the extent that there was any substance to speak of—was profoundly unsatisfying. (McCain’s “too early to draw that conclusion” answer to Stephanopoulos’s terror question, with no context, detail, or follow-up? What was that?)

It’s hard to conclude that today’s Twitterview was anything more than a shallow publicity stunt, aimed not at information or dialogue, but at making its participants—not only the (in)famously tech-reticent McCain, but his interviewer, as well—appear, you know, “with it.” The Claire McCaskillization of political discourse.

Which is not to say that Twitter has no place in politics (hey, I follow @clairecmc, and enjoy her tweets); but there’s a right way and a wrong (read: unproductive) way to use it. The platform is fantastic for real-time conversation and, more generally, sharing. And its strict word limits can have an admirable cut-the-crap-and-get-to-the-point effect—particularly productive among notoriously circumlocution-happy politicians. On Twitter, there’s literally no room for clever evasion. (Even if a politician managed to sneak such evasions into his tweets, the text-based nature of Twitter—since text simply lends itself to scrutiny more readily than does oral discourse—means he’s more likely than not to be called out later on.)

And yet. Today’s interview, looking beyond its overarching stunt-ness, is also a reminder of the very limitations of Twitter: the (in some ways profound) challenge of conveying substance in 140-characters-or-less. If the goal of an interview—especially one at this level, one conducted between a high-level politician and a high-level journalist—is to share information and have substantive discussions…then that goal, today, went largely unmet. (Stephanopoulos: “What worries you more: Pakistan or Iran?” McCain: “both. the challenges are different but both significant.” Riveting.)

Had Stephanopoulous asked the Pakistan/Iran question of McCain on, say, This Week, McCain would have looked, simply, ridiculous giving such a cagey answer. He would have had to give Stephanopoulos more. On Twitter, not only did McCain not have to say more; he couldn’t have. Sometimes you simply need the supreme threat of awkward silence to propel a conversation forward; that’s as true in media as it is anywhere else.

There’s a broader problem, too. When you’re interviewing a politician, in particular, the conversation may take place in real time; but the whole point is ultimately to transcend real time—to produce a document, in text or audio or video or what have you, that will endure. And that will, ultimately, foster accountability. But as an archival tool—as a mechanism not merely for discussion, but for preservation, of thoughts and information and interaction—Twitter leaves a lot to be desired. (Before I saw the transcript Stephanopoulos’s staff provided, to get a full sense of the interview, I had to cobble together individual tweets from McCain’s and Stephanopoulos’s feeds—a process which ranged from inefficient to full-on absurd.)

According to a recent study, though, a non-tagged link lives on Twitter for a grand total of five minutes; to combat its tweets’ own short life spans, Twitter relies on users to engage in self-archiving via hashtags. And if a conversation itself isn’t tagged—as the Stephanopoulos/McCain interview, to my great annoyance, was not—then, unless archived elsewhere, it disappears into the black hole of 140-character cyberspace. It fades, another words, into…Twoblivion.

Rendering the conversation itself, as a practical purpose—to the extent there was a practical purpose to today’s “talk” in the first place—virtually moot. (Yes, pun intended.)

Megan Garber is an assistant editor at the Nieman Journalism Lab at Harvard University. She was formerly a CJR staff writer.