Endangered black politicians?

In the NYT's politics blog, Katharine Seeyle says that Hillary Clinton's RFK reference was particularly bad because of the racial component of this election:

[O]n Friday, she made a reference to Bobby Kennedy’s assassination — a terrible choice of phrase in a presidential campaign that features an African-American candidate.

Was RFK black? Did I miss that? Just to be sure we got her point, she mentions it again:

[S]he used an eye-popping word in the context of a presidential campaign with a black candidate.

Okay, I just looked it up, and I'm reasonably sure Bobby Kennedy was white. So why the reference? Is there reason to believe that African American politicians are more prone to assassination than white politicians? That would certainly be an interesting finding, but is it true? Why is it just being assumed? Robert Farley addresses this issue with appropriate snark:

Every single President who has been assassinated in the history of the United States has been a white male. Every. Single. One. In fact, I have it on good authority that every single attempted assassination has been directed against a white male President. If history is any guide, Obama should be safe.

...indeed, with an assassination rate exceeding 9%, President of the United States would appear to be an extraordinarily dangerous job for white men. It would almost be irresponsible to elect someone other than a woman or non-white man.