Jesse, I appreciate your reply and the discussion.
Here's the image in question:

To me, that does smack of runaway slave imagery which is, almost by definition, racist. While that may not have been the conscious intent of the cartoonist, I most certainly perceive it that way. And frankly, I'm more than a little skeptical that the cartoonist was unaware of the imagery. Maybe s/he thinks it's provocative and somehow OK. I agree that it's provocative.
And I do agree with you that the basis of the cartoon is from the clip you posted. But I can't shake the feeling that if it were another candidate, the cartoonist would have somehow found different imagery to make his/her point.
Likewise, I suspect that by choosing that particular language, Senator Brown's campaign is multi-tasking -- making their central point of calling Mr. Mandel a liar and simultaneously reminding voters that are sensitive to it that, by the way, you do remember that Mr. Mandel is a Jew. Maybe they didn't mean it that way, nevertheless, there it is. And frankly, I'm noting the possibility that the reference is inadvertent out of intellectual discipline only.