Trump is regularly described as a narcissist by journalists, authors, and mental health professionals. 

Definition

Narcissism is a term that has both colloquial connotations and a psychiatric definition. Merriam-Webster’s Collegiate Dictionary defines narcissism as, "egoism, egocentrism," and "love of or sexual desire for one's own body."  The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) defines Narcissistic Personality Disorder as:

A pervasive pattern of grandiosity (in fantasy or behavior), need for admiration and lack of empathy, beginning by early adulthood and present in a variety of contexts, as indicated by five (or more) of the following:

1. Has a grandiose sense of self-importance (e.g., exaggerates achievements and talents, expects to be recognized as superior without commensurate achievements)
2. Is preoccupied with fantasies of unlimited success, power, brilliance, beauty, or ideal love
3. Believes that he is “special” and unique and can only be understood by, or should associate with, other special or high-status people (or institutions)
4. Requires excessive admiration
5. Has a sense of entitlement, i.e., unreasonable expectations of especially favorable treatment or automatic compliance with his or her expectations
6. Is interpersonally exploitative, i.e., takes advantage of others to achieve his or her own ends
7. Lacks empathy: is unwilling to recognize or identify with the feelings and needs of others
8. Is often envious of others or believes others are envious of him or her
9. Shows arrogant, haughty behaviors or attitudes
10. Often mild to moderate paranoia, that others are out to do him in.
11. Predominant “name dropper” boasting or suggestion association with people or affiliations of importance.

Timeline