The cartoonist fell into a trap I call a "remindsmeof." His comic was clearly about Congress, since President Obama didn't "write" the stimulus package. But the comic reminds the reader of racism and the risk of presidential assassination even though the cartoonist clearly wasn't addressing either topic. That was enough to get him into trouble.
In my early years of cartooning my editor rejected a few Dilbert comics because they were remindsmeofs. I thought it was overprotective and ridiculous. But I've since learned that you can't underestimate the public's ability to find offense where none is written. Now I recognize (usually) when I am about to blunder into a remindsmeof and I edit the comic myself. It saves time and trouble. When I offend, I prefer it to be intentional.