I actually agree that Race is a factor, but it has actually helped increase Obama's perceived lead in the polls. Its called "The Obama Effect" similar to the Bradley effect.
The liberal media and liberals activists have created a protective Halo around Obama because he is this "Black Savior" and average voters are push by Pop Culture to tell pollsters and their friends that they Blindly support the President.
But Obama's white support is very soft and unreliable. Most white voters care about the Economy, and 8% or 7.8% unemployment is still very bad and uncomfortable. Black unemployment is far worse and Black voters are equally upset about the economy and Obama's job performance.
Bottom line, Obama's supporters are subconcsiously lying to pollsters and won't remember to vote for him on election day, if they vote at all.
If race is a factor, it's because white voters who were, or are, Obama supporters, want to support him because he is part black. They assume that all things being equal, they would rather have the "black" candidate and prove that they're not racist. Ironically, most people who don't support President Obama, myself included, feel the way they do because they disagree with his left-wing policies, not because of his race. It was true when he first ran in 2008, and it's true again this year. If anything, there is a reverse Bradley effect: people vote for the black candidate in greater numbers to prove they're not racists. I don't think Tom Bradley necessarily lost because of his race, but it illustrates my point.
