Since 1944, when the movie “Gaslight” came out.
The term specifically refers to dimming and raising gas lights in a home to disorient the victim. It was subtle form of psychological manipulation employed by a socio-pathic villain in the movie who was trying to make his wife doubt her own judgment.
I'm not sure Jay Carney is in same situation; he's simply delivering valjar's messages. If anything he's the victim, disoriented by the reality slowly dissolving his illusions.