Greta van Susterin had an interesting theory: If Romney had been smoother/more convincing on this point, it might be just one more item that the audience might or might not remember. But by stumbling somewhat, Romney ensured that all the talk shows are going to keep talking about the Obama administration's bizarre comments about the Benghazi attack (not to mention that he went to a Vegas fundraiser the same day as the attack). And Obama would probably like to avoid those subjects.
True but it’s hard to believe it was planned. Maybe a fortunate, unintended outcome, but not planned. I think Obama won solely on the LOW expectations from the last debate. Debates are rarely game changers, but we did have one of those and Romney won it.