Politically partisan cognition as branding

With regard to politically partisan cognition, it's worth comparing emotional investment in commercial branding as a related phenomenon.

We are emotionally attached to the products we use regularly, so much so that we become defensive and tense when they are criticized, says a new study from the September issue of the Journal of Consumer Research. Interestingly, the more committed we are to a product – and thus the more incensed we are by any critique – the more counterarguments we are able to come up with.
"Less loyal individuals more readily agree with the unfavorable information and change their attitudes to be consistent with the new information," write Sekar Raju (University of Buffalo) and H. Rao Unnava (Ohio State University). "More loyal consumers question and argue against the information."

Given that emotional attachment can result in increased counterargumentation, it follows that political partisans would tend to counterargue rather than accept unfavorable information. It is therefore unsurprising that unpleasant facts may be hard for partisans to accept, at least initially.