Poisoning the well
Poisoning the well (or attempting to poison the well) is a type of informal fallacy where adverse information about a target is preemptively presented to an audience, with the intention of discrediting or ridiculing something that the target person is about to say. Poisoning the well can be a special case of argumentum ad hominem, and the term was first used in this sense by Catholic philosopher and Doctor of the Church John Henry Newman in his work Apologia Pro Vita Sua (1864).