Peter Hart, a Democrat on a bipartisan team conducting the Wall Street Journal/NBC News poll, estimates that 10% of current Democrats and independents who say they support presumed Democratic Party nominee Barack Obama may not be giving a fully honest answer, at least based on their responses to broader questions about race. "This election is exceptionally tricky," he says.

While most political pollsters say they don't find large numbers of people lying on polls, they are taking extra precautions. At CBS, pollster Kathleen A. Frankovic says she will ask voters whether they think most people they know would vote for a black candidate -- an indirect way to fish for racial bias. John Zogby, president of the polling firm Zogby International, is asking white respondents whether they have ever been to a dinner party where a black person was present. It only takes a handful of people hiding their true opinion to skew poll results, he says: "A small number can loom large."