Yesterday, I read Mark Mardell's BBC News article about Armenians in Turkey. I was sort of bored by it (no real new information nor insights) until the very end:

It seems to me that nationalism comes in two distinct types. One is fiercely proud of the achievements of the country, its history and language. The other is prickly, always looking out for insult and offence and its main motivation seems to be not pride, or even prejudice, but nursing old wounds.

Let's call it stabinthebackism, in memory of the Weimar Republic. Any gentle poking of fun, questioning of values or tradition is seen as the latest sign that the barbarian hordes are already inside the gates.

Replace "questioning of values" with "different political party affilation" and "barbarian hordes" with terrorists, and you pretty much get the current American political climate.