what makes Romney a weak candidate? he's a white male, smart, has money, all the essentials. what are the tick marks? that he's a Mormon, that he'd be vulnerable to certain negative attacks? true enough, but nobody is perfect and it's hard to imagine those issues overshadowing 9% unemployment and the general misery of American life for any decisive length of time.
He's not a "man of the people" in any sense and his backstory wouldn't inspire confidence in working class voters because he's Mormon, he's plastic, he comes from an elite political family and he has no real political conviction. He's essentially everything that the working class hate. While Romney is a great candidate for upper middle class/inner-suburban voters, I don't see him connecting with the disaffected, traditionally Democratic voters that Romney needs to win over.
Romney definitely deserves credit, he's managed to transform himself from the candidate of market ideologues and movement conservatives into the reasonable moderate with business experience.
pretty solid stuff though it should be noted that the Bushes are an elite political family as well - while W's rough edges allowed this to get sublimated not so for 41. Romney's class issues are a problem, but all that's required is that the underclasses simply stay home, not that they vote for him. if we have a return to 1996-level turnout the dent gets taken out of people who have no means.