Actually he did mention it. So I was mistaken. However this:

It saddens me, too, to witness the occasional exhibition of insanity from the Right, exemplified by No. 231 above. Such intemperateness is neither amusing nor helpful, and I regret its occurrence.

is about as weak an answer he could have given. A commenter on his site calls for the assasination of the President and the murder of millions of citizens and the best he can do is offer his regrets.