Gaslighting: A tactic in which a person or entity, in order to gain more influence, makes their victim question reality.
Gaslighters set up a precedent by telling blatant lies. Once they tell a huge lie, their victims are no longer sure if anything they say is true. One such lie, common to gaslighters, is to deny having said something that everyone knows, and can even prove they've said. The more they do this, the more their victims question their understanding of reality and start accepting the gaslighter's reality.
A follow-up ploy is to claim that everyone else is lying -- especially well-educated people trained and experienced in their specific professions. Eventually, it makes people turn to the gaslighter for the "correct" information, which isn't correct information at all.
There are conspiracists on this and other websites whose clumsy attempts at gaslighting should be obvious to everyone, yet there are still people who fall for their distortions and lies. Their intentional failure to "tell the truth, the whole truth, and nothing but the truth" serves only to reinforce my trust in traditionally reliable sources -- a multiplicity of media sources, legal authorities and medical experts -- all well-educated people trained and experienced in their specific professions.