From A Demon's Nest of Sentiments

People of a political kidney never can, never will at any time acknowledge the slightest possibility that they might be mistaken. That way lies the imminent crumbling of dogma, and the freakish implication that those holding opposite views could be, after all, tolerable, decent, even respectable.

http://www.gocomics.com/pibgorn/2014/06/22

This is a major change and problem with our divided political system, it's gotten to the point where they can't be friendly with each other out of the office. It's one thing to respectfully disagree with the opposition, it's quite another to consider them heretical and the antithesis of all good things.