What was thought to be a close race between Obama and Mitt Romney turned out to be both a popular vote and Electoral College blowout for Obama. In fact, Obama won the popular vote by about 5 MILLION votes. Obama won the EC with 336 compared to Romney's 201.
So, as much as polling cannot always predict the winner, it can also underestimate the winning margin of the favorite.
So, as much as polling cannot always predict the winner, it can also underestimate the winning margin of the favorite.