Conservative site Red State linked to a comment made by Herman Cain this morning:

The Republican presidential field’s Mr. Nice, Herman Cain, vowed to go on the attack early Wednesday morning, after an often sharp-tempered debate among the seven rivals.

“They’re getting on my last nerve,” he told CNN’s Carol Costello after opponents criticized his “9-9-9″ tax reform plan.

The minute Cain goes negative, he's lost*. The thing most Republicans find appealing about him is that he's bubbly, funny, and good-natured. He's a cancer survivor who seems like he's always looking on the bright side. If he starts whining like a big Santorum about all the unflattering attention, Republicans will flee, either back to Romney or on to the next Republican flash-in-the-pan. (Maybe it's time for Gingrich to have a moment in the sun? He hasn't embarrassed himself at these debates like the other candidates; I could see the electorate taking him out for a joyride before the voting starts in early January.)

* Please note that Cain doesn't have a chance in hell of winning the nomination, in any case. I'm just saying that this could be the thing that leads to his inevitable downfall.