David Roberts at Vox has a very perceptive piece on how to analyse Trump. ( Thanks Brad De Long).
You do not need a great intellect to be a political leader.
What you do need is to understand whether a policy can work and thus whether you should use your political capital to push it through and then gain more political capital when it works.
The problem with Trump is is he is so ignorant about policy he simply ignores advice from his advisors he does not believe in. His EO on refugees is a wonderful example of this. He was told there was NO evidence for his prejudice (which initially brought on the problems he incurs in the security and intelligence communities). Instead of listening to his experts he ignored them and pushed on regardless. History shows the EO was very poorly drafted by incompetents.