Agree DT has a personality order but would suggest narcissism is at the core. Mayo Clinic: If you have narcissistic personality disorder, you may come across as conceited, boastful or pretentious. You often monopolize conversations. You may belittle or look down on people you perceive as inferior. You may feel a sense of entitlement — and when you don't receive special treatment, you may become impatient or angry. You may insist on having "the best" of everything — for instance, the best car, athletic club or medical care.At the same time, you have trouble handling anything that may be perceived as criticism. To feel better, you may react with rage or contempt and try to belittle the other person to make yourself appear superior. 
I believe DT entered the race for adulation and attention.  Was surprised his 16 opponents evaporated so quickly. Enjoyed "the ride" until he realized it was possible he could win. Ramping up self destruct rhetoric. Did not, does not want to be President.