Wikipedia
Bulverism is a name for a logical fallacy that combines a genetic fallacy with circular reasoning. The method of Bulverism is to "assume that your opponent is wrong, and explain his error". The Bulverist assumes a speaker's argument is invalid or false and then explains why the speaker is so mistaken, attacking the speaker or the speaker's motive. The term "Bulverism" was coined by C. S. Lewis to poke fun at a very serious error in thinking that, he alleges, recurs often in a variety of religious, political, and philosophical debates.
Similar to Antony Flew's "Subject/Motive Shift", Bulverism is a fallacy of irrelevance. One accuses an argument of being wrong on the basis of the arguer's identity or motive, but these are strictly speaking irrelevant to the argument's validity or truth. But it is also a fallacy of circular reasoning, since it assumes, rather than argues, that one's opponent is wrong.