[The Romney Campaign] made three key miscalculations, in part because this race bucked historical trends: . . . .

 

2. Independents. State polls showed Romney winning big among independents. Historically, any candidate polling that well among independents wins. But as it turned out, many of those independents were former Republicans who now self-identify as independents. The state polls weren't oversampling Democrats and undersampling Republicans - there just weren't as many Republicans this time because they were calling themselves independents.