[Note from CAF: This is both a phenomenon and verb that is very useful to have available on the tip of your tongue these days!]
From Wikipedia
Gaslighting is a form of psychological abuse in which false information is presented with the intent of making a victim doubt his or her own memory, perception and sanity. Instances may range simply from the denial by an abuser that previous abusive incidents ever occurred, up to the staging of bizarre events by the abuser with the intention of disorienting the victim.
The term “gaslighting” comes from the play Gas Light and its film adaptations. The term is now also used in clinical and research literature.