...they believed the public/media polls were skewed - they thought those polls oversampled Democrats and didn't reflect Republican enthusiasm. They based their own internal polls on turnout levels more favorable to Romney. That was a grave miscalculation, as they would see on election night.
Those assumptions drove their campaign strategy: their internal polling showed them leading in key states, so they decided to make a play for a broad victory: go to places like Pennsylvania while also playing it safe in the last two weeks.
Those assessments were wrong.
Goodness knows that would have worked out reaaaaaaallllll well if they were at 1600 Pennsylvania Avenue.