See Gaslighting, by Stephanie Sarkis, PhD.
To Sarkis's explanation of gaslighting I would add that hurling accusations at truthful accusers creates a sense of chaos in which there is nothing resembling a common ground of reality. Instead, a state of interpersonal insanity prevails. At the heart of gaslighting, the gaslighter tries to make the target person feel overwhelmed and crazy. Then, when the target of the gaslighting explodes, the gaslighter can shake their head and say condescendingly: "see, you're out of control. You're nuts. You need professional help."
Certainly, Trump has created a field of unreality around him. Closer to Trump, presidential spokespersons do summersaults trying to keep up with his changing versions of the truth. In the larger social and political environment, much of what Trump injects into public discussion is flat-out, provably false.
A couple of days ago, Ivanka Trump said she was surprised by the level of visciouness she's encountered in D.C. She's been ridiculed for the extreme irony of her complaint, and mocked for her lack of awareness, but her statement also raises the possiblity that she's knowingly engaging in gaslighting, having learned at the feet of the master. Can she really be so unaware of her father's habit of vicious insult and defammatory statements about opponents and critics? He is, indisputably, the king of political viciousness.