First, it was not a gaffe in the Michael Kinsley sense of "when a politician tells the truth" because, IMHO, the controversial assertion was not entirely true. Here's it is, with runup:
CLARK: He has been a voice on the Senate Armed Services Committee. And he has traveled all over the world. But he hasn't held executive responsibility. That large squadron in the Navy that he commanded — that wasn't a wartime squadron. He hasn't been there and ordered the bombs to fall. He hasn't seen what it's like when diplomats come in and say, "I don't know whether we're going to be able to get this point through or not, do you want to take the risk, what about your reputation, how do we handle this publicly? He hasn't made those calls, Bob.Let's infer Clark's broader meaning from his immediate reaction to Schieffer's words: fiercesome combat experience (or any combat experience) is not "a qualification" to be President. Plainly it's not a necessary qualification. Neither Reagan, FDR, Lincoln nor Jefferson had it. But it's certainly a qualification. Combat experience informed John Kennedy's and George Bush Sr's feel for the capabilities and constraints of the military. More generally, being forced to make decisions in the extreme stress of combat, or even simply endure, surely puts all subsequent experience in perspective. As one young Captain, veteran of two tours in Iraq, told the New York Times' Michael Kamber, "“We’re leaders proven under fire...put me in the most stressful corporate board meeting and I’ll laugh.” That's not to say that the pressures outlined by Clark in the passage above would make the captain laugh. But his experience -- if it hadn't traumatized or destroyed him -- would equip him to handle those pressures.
SCHIEFFER: Can I just interrupt you? I have to say, Barack Obama hasn't had any of these experiences either, nor has he ridden in a fighter plane and gotten shot down.
CLARK: I don’t think getting in a fighter plane and getting shot down is a qualification to become president.
But Clarke's statement was also not a swiftboating. He went out of his way to say that he honored McCain's service -- he did not denigrate or minimize it. To the extent that it sounded as if he did it was in the near-exact echo of Schieffer's statement, "nor has he ridden in a fighter plane and gotten shot down." Clark was simply asserting that Schieffer's implication -- that such experience qualified McCain to be President - was false.
Finally, Clark's whole argument was not particularly logical, and certainly not politically acute. Clark detailed the executive experience McCain lacks, but of course Obama's executive experience deficit is larger than McCain's. McCain may have only run a squadron that was not in combat, but Obama has run nothing but his campaign (extraordinarily well, of course).
What the performance was was typical Wesley Clark - focused, articluate, and oddly tone-deaf.