Blogger Brendan Nyhan conducted the study with students from Duke. His hypothesis: a negatively phrased correction ("he is not a Muslim") would be less effective than a positive one ("he is a Christian"). But, hah, neither one was remotely effective at convincing participants that the President is a Christian. Until they added... a black person!
However, our hypothesis that the corrective affirmation would successfully reduce misperceptions was only supported when a non-white experimental administrator was present, suggesting a strong social desirability effect on the acceptance of corrective information. In addition, three-way interactions between the corrective affirmation, race of administrator, and party identification suggest that social desirability effects were more prevalent among Republicans.
But when fellow typical white people tried to convince Republicans that Barack Obama is a Christian, it "caused a backfire effect in which GOP identifiers became more likely to believe Obama is Muslim and less likely to believe he was being honest about his religion."