Nothing at all, in terms of Salt Lake Tribune cartoonist Pat Bagley's drawing ability.
That is a really nice drawing of Parks and of Breitbart and of Sherrod—Bagley does a great job of making Sherrod look at once like an inanimate object of the sort one might push or roll around, yet she's just animated enough to display a surprised expression. I like the period details invested in each bus, indicating which time period each is from, and I even like the slightly messy, dashed-off look of the colors as seen above (although my hometown paper, where I saw the cartoon earlier today, ran it in black and white).
The connection between "back of the bus" and "under the bus" in terms of racial politics in America seems like a sensible kernel with which to start a political cartoon on the subject, but Bagley seems to have garbled something in the final execution.
The expression "to throw someone under the bus" means to scapegoat or blame an ally, or at least someone who can be seen as an ally or as on the same team as the person doing the throwing (or pushing or tossing). Whether the throw-ee is thrown under the bus with good reason or not, or whether the thrower was justified to be throwing them at all, doesn't really matter in the usage of the phrase. The sole requirement is that both the thrower or throw-ee were on the same bus, moving the same direction. It denotes a betrayal or abandonment of the person thrown under the bus.
So why is the man labeled "Breitbart" in this cartoon at all?
Conservative blogger Andrew Brietbart kicked off the fast-moving media storm that resulted in Department of Agriculture employee Shirley Sherrod being fired, yes. He did so by editing a March speech she gave in such a way to suggest, to Breitbart and those who, like him, are concerned that the NAACP, of which Sherrod was a member, may be for the Advancement of Colored People as their name suggests, but only at the expense of the Color-less People. That is, Sherrod, who is black, is racist against white people, and this was proven by a not-terribly-damning-even-out-of-context bit of a speech she once gave.
Long story (that you probably already know) short, the NAACP condemned Sherrod and USDA Tom Vilsack fired her, based on Breitbart's claims, which no one bothered to check out for a good 24 hours or so.
So one could say that the NAACP threw Sherrod under the bus. One could say that Vilsack through her under the bus. Or the USDA. Or the media. Or the Obama administration. Or Obama himself (assigning blame to him personally might not be accurate per se, but it would be accurate enough for a political cartoon, in which a president can symbolize his party or administration).
But Breitbart? He didn't throw Sherrod under the bus. He's just about the only person or institution mentioned in this post who didn't throw Sherrod under the bus. If he has a place in the bush-throwing-under metaphor, perhaps one could say he indirectly suggested she be thrown under the bus, but to suggest that he did the throwing himself suggests a closeness between he and Sherrod.
So despite some wonderful drawings, I think this political cartoon is "wrong"...not in the opinions it expresses (which I don't quite understand anyway), but in its reporting of the situation it uses as its basis.
Of course, that's assuming that the right half of the cartoon is meant to suggest the expression "to throw someone under the bus."
Maybe the message of the cartoon is simply that in in the past, much of white America was institutionally discriminatory against black ladies when it came to public transportation, whereas today we may have gotten past that, but Andrew Breitbart still runs around pushing down middle-aged black ladies, and the Fox News bus then tries to run them over.
If that's the case, then this political cartoon makes perfect sense.
The above version of Bagley's cartoon was taken from Daryl Cagle's Political Cartoonists Index. Click here to see examples of the various ways various political cartoonists approached the Sherrod/Breitbart fiasco. More than one used bus imagery, and John Darkow even used a back of the bus/under the bus formulation, only he attributed the pushing of Sherrod under the bus to Obama and the NAACP.