Santorum was, perhaps, the strongest -- the question is whether it will matter. This was his best debate ever, and he left track marks on Romney and Gingrich.
Romney did a much better job defending himself and his record, although Rick Santorum ably tried to exploit some conservatives' discomfort with his record. He stumbled a little over his tax returns, but at least seemed unapologetic about his success. Who knew he hadn't inheirited anything from his parents -- that he earned all his wealth himself? He needs to let that fact get around. His closing state ent was the best of the night.
Gingrich's best moment came when he attacked the press. But he lost all credibility when he (on the same day a personal bombshell exploded on his own head) raised the question of the "risk" of Romney's tax return -- and came across as ungracious In the extreme. Santorum's exchange with him about grandiosity was a killer. On top,of everything else, when he's not at peak form, he seems to drip with some of the condescension that Americans grew to dislike with both Al Gore and President Obama.
(Update: Gingrich just complimented John King's conduct of the debate. So was his rant at the debate's outset just red meat for the masses? Or does he have a deep need to suck up to the press after bashing it?)
Ron Paul was . . . Ron Paul.