From an ideological point of view, intention is practically beside the point. Meaning is created in the interpretive interaction between a reader and the text produced by an author; the intentional meaning expressed by the author may not necessarily be apprehended by the audience if not communicated well in the writing, and the people interpreting the text are not mind-readers. I know this from experience....in high school I submitted a story in the writing club that was thought to be highly offensive, and I had no idea that it would be taken that way, and it certainly was not my intention. But seeing it from the point of view of the reader, I realized that there was no way the reader could have interpreted the story the way I intended it. So I have no idea what the author here intended, but does it really matter? The job of the editor was to review the piece and deem whether it was suitable and whether it could have caused offense among the readership -- and clearly the editor either failed to see how offensive this cartoon is or endorsed the offensive meaning.
Analytically I could make a few observations. Texts are polysemeous and may mean different things to different people, or within different situations and contexts -- especially if they contain ambiguous features or characteristics that conflict with a perceived meaning. The cartoonist could have had "Pelosi", "Congress", "Obama", or whatever on the dead chimp's chest (this is the usual convention), but did not; he left the identity open to interpretation. The cartoon juxtaposes two unrelated news stories in a bizarre way -- in just what way is the stimulus bill like the chimpanzee that went on a tragic and wild rampage? Is the cartoonist trying to suggest that the legislation was a violent attack on the US economy and taxpayers, was that the intended point? But that doesn't seem likely since there is nothing that happened that corresponds to what the cartoon actually depicts -- the shooting of the chimpanzee. That makes it harder to relate the two news stories. But it makes partial sense if the cartoon is interpreted as referring to a potential future assassination, as the dead chimp is directly identified as "the one who wrote the stimulus bill". The thought that the cartoonist is talking lightly about assassination alone is cause for offence. But who does the chimp represent and who is being assassinated? The features here are conflicting. It was Congress that wrote the bill, the verb used in the caption, not the President. And yet, it is hard to believe that the cartoon is talking about something so unusual as the assassination of all of Congress, or all the Democrats of Congress, or even the leadership. The victims of assassination tend to be the holders of the Executive Office in common thought; everyone can name at least two if not four or more Presidents that at least have experienced an attempt. And the individuality of the President fits better with the individuality of the chimp than a collective entity like Congress or Congressional Democrats. The popular meme that compared the last President (George W. Bush) with a chimp also reinforces this interpretation, even though Bush is not the President presumed by this interpretation. But what especially reinforces this interpretation are the various racial discourses that also fit well with an interpretation that Obama = the dead chimp. Foremost of these is the long history of whites dehumanizing blacks as apes, monkeys, subhumans (such as the Gollywog cariacture), and so forth. There was the controversy from the campaign of people making T-shirts depicting Obama as Curious George. So the identification of Obama = dead chimp is one promoted by this discourse. Then there is the theme of cops shooting the chimp. This indirectly reinforces the interpretation of chimp= blacks in two ways: first, there is a racial discourse about blacks being more likely to commit violent crime (which is evoked by the implied violence of the chimp against the real-life victim), and second there is the history of police brutality against blacks (which is evoked by the use of lethal force against the chimp and the rather cavalier/jocular remark made by the cops to each other). So in favor of interpreting the dead chimp as Obama, we have 1) the racial discourse of blacks being monkeys and apes, 2) the fact that Obama was depicted by some racists as a monkey in the campaign, 3) the history of police brutality against blacks, 4) the racial discourse of blacks being violent criminals, 5) the theme of assassination more naturally pertaining to the office of President, and 6) the individuality of the chimp being more naturally associated with an individual referrent, such as the President. Against this reading, we have 1) the chimp was depicted as the one who wrote the stimulus bill, and ..... is there anything else? And even this point can be pressed to conform to the Obama interpretation, as Obama did write his name on the bill to sign it into law.
So whether or not the cartoonist intended the cartoon to refer to Obama, the explanation that makes the most sense of the cartoon's features is the one that interprets the cartoon as referring to Obama -- but this too is problematic. If this is not what the cartoonist intended, he did a poor job in communicating his thought. The cartoonist and the editor in their public statements yesterday also did not apologize or explain what the cartoon was supposed to depict (the cartoonist's statement itself is ambiguous).