"Given Obama's racial background," writes Brendan Nyhan, "the danger is that these attacks will be used to trigger ugly racial stereotypes about him, particularly once Republicans shift from bong jokes to talking about cocaine, which Obama admitted to trying in his first book."
I dunno about this. It seems to me that if you have an African-American candidate whose admitted to past cocaine use, that attacking him for past cocaine use is less an appeal to ugly racial stereotypes than a straightforward attack on his past drug use. An appeal to ugly racial stereotypes would be implying that a black candidate must have used cocaine in the past because, hey, that's what those people do. I don't personally have any problem with the idea that of a president who used cocaine in the past (though, admittedly, the George W. Bush experience hasn't been very pleasant) but insofar as some voters do have a problem with it, they're entitled to have a problem with it irrespective of the candidate's race.