(Or, why I would hold my nose and support Romney)
Politicians: Their guys (and gals) are all liars. Our guys always tell the truth. So we tend to believe our guys. As a result, we detest the opposition and our own standard-bearers are typically a shade less evil or else completely virtuous.
Take Mitt Romney. Having spent the primaries in the Not Romney camp, every previous turn he took claiming he didn't want to be Reagan rang true for me. He's supposed to be in my camp so I took him at his words. He was a progressive. Those words were not good, so I didn't like him.