He's never been good at adapting his stump speech content to the debate format.
His intimating that W was responsible for 9/11 isn't smart. I've no doubt some PC "don't profile Arabs" permeated the Bush Admin, but it's not generally accepted that Bush caused it.
I think that isn't accepted at all. The charge is that GWB could have done more to stop it. There were a number of red flags thrown up, not acted on. "The wall," described by Jamie Gorelick, could have been demolished before the WTC was. Not saying it's a fair argument, but that's the nature of the argument.