Last month's edition of Harper's had an interesting piece on the history of the "stab in the back" myth in America:
Every state must have its enemies. Great powers must have especially monstrous foes. Above all, these foes must arise from within, for national pride does not admit that a great nation can be defeated by any outside force. That is why, though its origins are elsewhere, the stab in the back has become the sustaining myth of modern American nationalism. Since the end of World War II it has been the device by which the American right wing has both revitalized itself and repeatedly avoided responsibility for its own worst blunders. Indeed, the right has distilled its tale of betrayal into a formula: Advocate some momentarily popular but reckless policy. Deny culpability when that policy is exposed as disastrous. Blame the disaster on internal enemies who hate America. Repeat, always making sure to increase the number of internal enemies.
Read the whole thing - and then read the wikipedia article on the parallel phenomena in Weimer Germany (the original dolchstosslegende). There, the myth of the "stab in the back" was a significant propaganda tool in the rise of the Nazis and the demonisation of socialists, liberals, and Jews. Then look back at the US and the way right-wing voices there are openly preaching the elimination of liberals, while voices critical of the Bush administration find themselves receiving white powder in the mail. It's a worrying trend, and they haven't even officially lost the war yet.