Frida Ghitis has written a pretty good opinion piece illustrating how Our Donald is using the Gaslight Gambit to screw with the collective American mind.
Donald Trump is 'gaslighting' all of us
Here is a good, non-technical explanation of the term, from Wiki:
It's a technique that is far more widespread than most people realize. Here is an excerpt from the Wiki article:
Sociopaths and narcissists frequently use gaslighting tactics. Sociopaths consistently transgress social mores, break laws, and exploit others, but typically are also convincing liars, sometimes charming ones, who consistently deny wrongdoing. Thus, some who have been victimized by sociopaths may doubt their own perceptions. Some physically abusive spouses may gaslight their partners by flatly denying that they have been violent. Gaslighting may occur in parent–child relationships, with either parent, child, or both, lying to each other and attempting to undermine perceptions.
Gaslighting also occurs in examples of school bullying – when combined with other psychological and physical methods, the result can lead to long-lasting psychological disorders and even progress into illnesses such as depression or avoidant personality disorder. Gaslighting describes a dynamic observed in some cases of marital infidelity: "Therapists may contribute to the victim's distress through mislabeling the woman's reactions. […] The gaslighting behaviors of the spouse provide a recipe for the so-called 'nervous breakdown' for some women [and] suicide in some of the worst situations."
That's Trump to a 'T.'
As Ghitis points out in her opinion piece, Trump is an accomplished Gaslighter; he pulled it off continually throughout the campaign, and is still doing it today. Her article is well worth a read.