Questioning the partisan motives of a citizen who criticizes the government. Big no-no. Don’t even think about it, or you will find your eye on the Sparrow when the going gets narrow.

And yet. While one wonders where Ryan Sparrow would ever have come up with the idea that “He’s a Liberal” is a pertinent comeback to any policy critique (cough), one must entertain the possibility that he has simply learned his lessons well. Why, just as a f’rinstance, here’s one of Sparrow’s colleagues dismissing a constitutional criticism on the grounds that the critic had donated to the Liberals (while preferring the testimony of a scholar who had received money from the Harper government).

One presumes readers can come up with more examples.

Now, it is true that neither Linda Keen nor Errol Mendes is the father of a slain Canadian soldier, so Sparrow’s dig at Jim Davis has a certain gruesomeness to it that my other two cases don’t. (Its timing is poignant, too. I seem to recall events on a previous Sept. 11 that offered lessons in the value of democracy and political pluralism.) But the modus operandi is clear, field-tested, and apparently freshly off-limits as of this morning: when attacked, go ad hominem. Poor Ryan Sparrow: He was well trained, and he was only applying lessons learned.