In the last two days, six new polls of Ohio voters have been released, five of which favor President Barack Obama, by leads of 6 points, 4 points, 4 points, 3 points and 2 points. The last reports a tie, from right-leaning Rasmussen, which gave former Gov. Mitt Romney a 2-point advantage last week. Obama now has a 3.1 percentage point lead in Pollster's average for Ohio and a 2.9 percentage point lead in the RealClearPolitics average for Ohio.
A 3 percentage point lead is hardly an insurmountable margin for Obama. But it has been so consistent over the past several weeks that Romney ought to be hoping that the polls favor Obama on a systematic basis by overestimating the turnout of respondents with demographics that favor him. This is certainly possible, but it would mean that many different polling institutions are making similar mistakes. The outcome of Ohio, then, will be as much a referendum on the art of polling as it will be on the art of the presidency.
Sources: Betfair, Intrade, IEM, HuffPost Pollster and RealClearPolitics