From Wikipedia:

“Poisoning the well (or attempting to poison the well) is a rhetorical device where adverse information about a target is pre-emptively presented to an audience, with the intention of discrediting or ridiculing everything that the target person is about to say.”

This is another rather common way to overcome an argument that one cannot defeat by logic or reason.  It is not quite as useful as some other methods in a live debate, because it is more easily recognized and countered as a form of “ad hominem” attack — the target can easily point it out to the audience as empty rhetoric — though a skillful debater can shut the door to this defense.  But especially where the target does not easily have access to the medium (i.e. an essay appearing in a source the target cannot access), it is again quite useful.

A summary of this form of fallacious argument:

Discredit the other person before they speak. Or discredit the topic or  argument that they may support.  Call them names. Talk about  their supposed lies. Show them to be  unworthy. Tell how they are unintelligent, crazy or otherwise undesirable, inferior and not worth listening to, let alone believing.

Poisoning the Well is closely related to Appeal to Ridicule.