Shankar Vedantam explains two studies on the smear campaigns of 2008 and why they worked:
The researchers found that when they subliminally flashed the name Obama before [McCain] volunteersthe flashes were so brief that the volunteers did not notice the flashthis 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 the subtle conflation of Obama with terrorists - one of Palin's disgusting tactics in 2008 - was so powerful. I have no doubt that, as Steve Schmidt ruefully concedes, Obama's landslide would have been much larger if she had not been on the ticket. Because she will say anything, and because she sees the entire world as "us" vs "them".