Apparently, Kathleen Parker felt obligated to raise the McVeigh question in the first paragraph of this piece, as it was designed for the 15th anniversary of Oklahoma City, In reality, most of the rest of the piece makes the case that we could be headed for another John Hinckley.

Both notions are prepostorous; neither man was motivated by overheated political rhetoric. McVeigh's anger was driven by the (Clinton administration) botched Waco raid. Hinckley, as Parker points out, was fueled by a warped affection/desire for Jodie Foster, which leads to this rather strange observation:

If Jodie Foster could  bestir the imagination of Hinckley, a Sarah Palin in the Internet age could move regiments.

And then there is this even stranger observation:

What is clear is that technology and social media have empowered the least sane among us and amplified their voices. Thus, a random racist at a tea party rally suddenly becomes the face of a group of people who are, on the whole, decent, law-abiding citizens with legitimate concerns about government expansion and the inherent erosion of individual freedom.

1) How often has this happpened?

2) If he's a random racist voice and most in the group aren't like him, what impact will he have?

Most of this discussion remains theoretical because most tea parties have been tame affairs. The reality is many Republican elites are made uncomfortable by the tea parties, much the way they were made uncomfortable by the rise of Sarah Palin. The Tea Party people aren't Kathleen Parker's people or George Will's people. But they are the foot soldiers of the current conservative movement. Liberals often claim conservatives aren't comfortable spending time with minorities; a mostly false stereotype. However, that does seem to be the way Republican elites feel about the Tea Party movement.