This fallacy shifts an argument from the point being discussed (ad rem) to irrelevant personal characteristics of an opponent (ad hominem). Instead of addressing the issue presented by an opponent, this argument makes the opponent the issue. It shifts attention from the argument to the arguer; instead of disproving the substance of what is asserted, the argument attacks the person who made the assertion.

Ruggero J. Aldisert, Agatha D. Aldisert, Logic for Lawyers- A Guide …, loc. 1049