Presidential Candidate John Edwards presents an uneven expression, leading to distrust. Neuroscience can show us that true emotions play on one side of the face and masking on the other. I forget which side is which for the "real" emotions but this is why Bush's smirk makes us uncomfortable.
Reason and logic are sometimes not used as much as gut feelings and emotions, especially with politics.
The role of semantics and neurology in politics is something I'm interested in. Drew Westen, a professor of psychology at Emory University, has a book, “The Political Brain: The Role of Emotion in Deciding the Fate of the Nation,” and it is one that might make for good reading.