The phrase "to poison the well" means to say or do something that makes others lose trust in a person or idea before they even have a chance to consider it fairly. It is like tainting a water source, making it unfit for drinking. Full definition
Your body can fight off food poisoning better when it's minimally affected with smaller portions versus a very large meal. (travelinsurancereview.net)
Not only are too many leaders trying to hide or otherwise deny the good scientific evidence of human - driven climate change, they are also actively involved in poisoning the well of public discourse by strategically disseminating disinformation. (dotearth.blogs.nytimes.com)