Why are you all thinking Romney is doing bad? If anyone the worst one on stage it's Cain right now.
My perception: Cain is looking irrelevant and silly, and probably helping his gradual Perry-style bleeding. Romney is making a mistake by poking at Huntsman especially, but in general keeps starting fights where he ends up looking weak. The people he's fighting for are demonstrating his appeals (moderation, calmness, certainty, cogency) better than he is.
That said, Perry's strong performance tonight makes for a pretty weird dynamic, and might be the best thing Romney has going tonight, in terms of polling repercussions.