“Blood libel” was a series of actual false accusations that morphed into a general term. A blood libel is defined as a serious false accusation. It is derived from ancient and not so ancient accusations that Jews drank the blood of Christian babies. The belief survives today in the minds of some extremist Muslims.
If someone said that Obama told a group of Philadelphia supporters, referring to Republicans, “If they bring a knife to the fight, we will bring a gun”, it would not be blood libel because it’s true. But if in turn, it was claimed that his rhetoric caused the Gifford shooting it would fit the definition of the term “blood libel” – a serious false accusation. That’s what Sarah Palin suffered.
Within the Jewish community, the term blood libel has connotations not so widely known elsewhere. We know that it was an unfortunate choice of words because it raised the sensitivities of some people, understandably so. It would have been better had she called the accusations “cheap shots”.