I'm not too worried about Brokaw tonight. The rules don't really allow him any latitude for barbecue beyond the initial question selection.
Brokaw selects the questions to ask from written queries submitted prior to the debate, according to the "contract."
An audience member will not be allowed to switch questions. Under the deal, the moderator may not ask followups or make comments. The person who asks the question will not be allowed a follow-up either, and his or her microphone will be turned off after the question is read. A camera shot will only be shown of the person asking -- not reacting.
So Brokaw will basically be allowed to say two things: 1) "Our next question is from [blank]," and, "Senator [blank]?"
Remember four years ago in the town hall debate when President Bush went nuts on Charlie Gibson -- shouting gibberish about Alexander Kwasniewski? Maybe McCain will have a schizoid embolism tonight.