The issue is that only a small part of the country was subjected to the negative anti Romney barrage over the summer. If he loses there, but does much better than expected in states like CA, PA, CT, etc. .(but still falls short), that’s how you’d end up with a split.
Historically speaking, the odds of a split are low.
Look across the river in New Jersey, where college educated whites dominate (Hunterdon, Monmouth, Morris) Romney won. He lost the ethnic Asian and Jewish suburbs in Bergen and Middlesex, along with the blue collar white suburbs near Philadelphia (so much for blue collar white Catholics being "natural conservatives").
College educated single women and Asians are a problem, however, although the latter are overwhelmingly concentrated in Cali, Hawaii, NY, NJ, etc. Yuppie/hipster whites may be a common site in New Brooklyn and Portland, but are a tiny minority of the white electorate as a whole. The Democratic share of the white vote is shrinking, not growing. We needto see how we can get more whites in Ohio, Wisconsin, Iowa, Michigan, and PA to vote GOP.