They say that Obama didn't write the Stimulus Bill. But the average, dumb racist white person doesn't know that, and will see Obama, not Congress as the chimp. The cartoonist likely knew this, and knew he would get laughter from a racist crowd, which may have been who he wanted to appeal to.
And racism aside, it's also not in proper taste to laugh at the incident that inspired the cartoonist to draw a chimp being shot by an officer. I don't see anything funny about a woman having most of her face chewed off by a chimp. Anyone who does is sick IMO.