Here is a good theory. It goes like this: The economy argument may not be as powerful as Rmoney thinks it is because America is not one economy but many. The economy for middle-class white voters is not the same as the economy for blacks and brown voters. The first group is in the economy that's enjoying a recovery, the other two groups are in the economy that's still depressed. Rmoney, however, is speaking to white voters as if they are in a depressed economy, but the people who actually are, brown and black folks, he is neither addressing or winning over.
One of the ironies of the 2012 presidential campaign is that the incumbent president has benefited from strong support among many of the constituencies that have been hardest-hit by high unemployment levels, particularly black Americans and Latino Americans. This has left the Romney campaign in the position of having to win over voters who've fared relatively well since 2008.