By my informal count, at least six times McCain said Obama "doesn't understand" this or that. I find that condescending, but maybe it's working with swing voters. I dunno.
What I do know is that Obama did not come up with the caustic, repeatable sound bite. Can somebody explain to me why Obama didn't interrupt just once to say, "You know, Senator McCain keeps saying I don't understand this or that, but on the biggest foreign policy and military decision of the past 40 years -- the Iraq invasion -- the senator got it wrong. Repeat: Wrong. So he ought to save all his condescending lectures about who understands what, because he didn't understand what was at stake in Iraq, and that misunderstanding cost us 4,000 lives and a trillion dollars."