Shankar Vedantam talks about studies of both campaigns from the 2008 presidential election:
The researchers found that when they subliminally flashed the name Obama before [McCain] volunteers—the flashes were so brief that the volunteers did not notice the flash—this unconsciously activated words such as Arab, turban, and mosque in the minds of McCain supporters. Likewise, subliminally flashing the word McCain unconsciously activated words such as senile, dementia, and Alzheimer's in the minds of Obama supporters. The same thing did not happen when volunteers were flashed the name of the candidate they supported. The slur-related words were activated only by unconsciously reminding them about the candidate they opposed.This is why I always say that "both sides do bad things" and that if anyone says that their side does not that they are inveterate liars. But I also say that "one side is better at saying bad things and making them stick". Ask yourself which is more likely to be true: that John McCain is losing control of his mental faculties because he's growing old or that Barack Obama hates America because he's a secret Muslim?