It's fun to contemplate the possibility:

Psychiatrists commonly encounter deception in the emergency department. This article presents the case of a patient who presents to the emergency department with an unusual and elaborate web of deceptions along multiple themes including feigning medical illness, multiple losses, and grandiose academic and athletic achievements. We review the clinical characteristics of pseudologia fantastica and discuss how this patient's constellation of malingering, factitious disorder, and personality disorder suggests this diagnosis.

Pseudologia fantastica, a fascinating psychiatric syndrome where patients represent certain fantasies as real occurrences, has received little attention in the English literature: there are fewer than thirty case reports in the English literature. Pseudologia fantastica goes by multiple different names including pathologic lying and mythomania. In this case report and discussion, we begin by providing a case that illustrates pseudologia fantastica and then discuss the phenomenologic, nosologic, psychodynamic, and treatment issues of this construct.

From a Case study here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5442346/

BBC radio actually devoted an entire program to "Why Does Donald Trump Lie?" I wish I could remember the name of the psychotherapist they interviewed towards the end. He thought that Trump lied out of deep issues related to his childhood and that he craved attention--even negative attention.

CORRECTION: Actually, the psychotherapist added that Trump lies to "get inside our heads" but also that the lies he told were lies that he wishes were actually true, but he couldn't tell if Trump believed them or not.