I'm not joking about this: in the wake of her catastrophic performance in the Katie Couric interview, Sarah Palin has set expectations so low that she is very likely to do "surprisingly" well against Joe Biden on October 2.
That is, to seem more flustered and incoherent than she did against Couric, Palin would have to move herself into "Eagleton zone," where her presence on the ticket would no longer be sustainable.
Any informed-seeming answer she gives will be her first such answer under press questioning -- which in practice means the Gibson and Couric interviews. This is especially true if it's to a "but what about....?" or "are you saying...?" follow-up question. Those follow-ups, from Couric, were the truly lethal ones. Odds are that Palin will manage to handle at least one exchange of this sort, maybe more, and therefore show "improvement" and beat the expectations game.
Either that, or she and the ticket are mortally wounded.