Trump action is easily explainable if you had experience with someone with personality disorder and if you have the 'chinese' culture fabric in you. Psychologists suggested that some culture is more susceptible to personality disorder and as a Vietnamese origin, I fully concur this. It comes down basically to a person living in his own reality and in that reality, the only thing that is important is the perception of people about them or his image hence the 'definition' of sucess or greatness. However, since there's no place for morale in this 'the winner takes it all' mode, the proof of success is never a great story to tell but the results to show. Most of the time, it's material or money used to demonstrate the success but the story behind it is hidden voluntary. The road to glory from those people is not something they want people to have a clear look.
The brain will be conditionned to work permanently in PR mode but only in a very narrow time space. Everything said and done or expressed orther wise are purely on an impulsive reaction to improve or gain a 'battle'. Everything is treated like a battle but the war itself is overlooked or often even not clear. It is 100% certainty that Trump don't really remember what he said or doesn't really care but will use the benefit of a declaration if he ever found out that advantage him ex: not going into Iraq (he said the opposite before that). An analogy is a guy guessing almost all numbers before the roulette spined and then told people how he knew it would happen.
It is also very important to win the 'battle' vs anything is front of him or deflect 'bad' stories or danger to the hidden reality (to him anyways). It is a self secure feeling to his own personality cult. To prove to himself and his followers that he's not to mess with. It is not a hasard that a guy who pride himself as a 'builder' or 'development' would overuse a word like 'deal' to sell himself to public. In his mind, the ability to make a deal is the greatest attribute as a business man, it is the 'general' ability to win battles. A con artist mindset. Note that the 'war' in 'deal' is not really talked about: being rich/successful will cover that.
Trump also thinks he's smart because he is actually the alternative fact thinker. He doesn't see what happened as most of people and what he said / tweeted is an invitation to people to alternatively understand his message. Basically, in his world, it is normal that people is 'dumber' and don't see the 'truth'. It is also very 'natural' to him to shout out 'fake news' or 'alternative facts' because his brain is already accepted his version as the reference.
If you come from those regions of the world where 'smartness' is defined by people getting on top of others with no regard to morale, you will recognize Trump instantly. He is exactly one of those too many people that I have met in my life who aren't necessary a celebrity or wealthy personality but are programmed to work exactly the same way.
It is also dangerous that these people are easily manipulated themseves, they always think that they have that ability to 'use' people but they are also the easiest prey if you know how to play them.
What is astonishing is that you realized that he was actually elected as the president of the USA, a country in which the foundation fathers put everything they could (learned and known at that time) in place to prevent a disaster coming from the most dangerous threat of all: human.