But Donald Trump is in a different category. The sheer frequency, spontaneity and seeming irrelevance of his lies have no precedent. Nixon, Reagan and Clinton were protecting their reputations; Trump seems to lie for the pure joy of it. A whopping 70 percent of Trump’s statements that PolitiFact checked during the campaign were false, while only 4 percent were completely true, and 11 percent mostly true. (Compare that to the politician Trump dubbed “crooked,” Hillary Clinton: Just 26 percent of her statements were deemed false.)
Those who have followed Trump’s career say his lying isn’t just a tactic, but an ingrained habit. New York tabloid writers who covered Trump as a mogul on the rise in the 1980s and ’90s found him categorically different from the other self-promoting celebrities in just how often, and pointlessly, he would lie to them. In his own autobiography, Trump used the phrase “truthful hyperbole,” a term coined by his ghostwriter referring to the flagrant truth-stretching that Trump employed, over and over, to help close sales. Trump apparently loved the wording, and went on to adopt it as his own.
https://www.politico.com/magazine/story/2017/01/donald-trump-lies-liar-effect-brain-214658