back as far as about 2008 with one article with a date of 1998 that seems to have been taken off the 'net.

I've found its use with regards to President Obama and against the leftists since about 2008. I really don't want to link to those sites here. Some of them are pretty ugly.

Apparently, the "far" right (as versus, what, the moderate right?) have been using the "blood libel" phrase for a few years now beginning in the more fringe groups of the anti-choice movement.

This may be the first time it's been said aloud by one on the national stage but apparently it's been percolating through the fringe wing for quite some time.

There is a reason we need to keep ever vigilant and do opposition research.

edit to finish my thought.

Given this information and her association with some of the more fringe groups on the right, it's highly unlikely sarah was not aware of its definition or use.