Poisoning the Well is an attempt to bias an audience’s opinion before an opponent has had a chance to state their case.
This practice comes in a variety of flavors, and not tasty ones like guava or mango, probably most often taking the form of an ‘Ad-Hominem’ attack. Poisoning the Well is done in order to call into question any later statements from the opponent.
“He is going to say he didn’t use performance enhancing drugs. How are we going to believe him? His whole team used them!”
“Only a moron will believe this story.”
The first example of the term ‘poisoning the well’ being used in this context was by John Henry Newman in a published defense of his religious beliefs, ‘Apologia Pro Vita Sua’.The origin of the term comes from the Medieval, anti-Semitic notion that Jews spread Black Death via communal drinking wells. Needless to say, germ theory was not a thing at the time, and superstition most certainly was… and still is…