Just compare the off-script and on-script Trump. When he's babbling about things coming directly from his brain, he sounds like an immature 11 year old with no context, no focus, no purpose. When he reads from his teleprompter, he can regurgitate figures, sometimes a bit of history, even correctly state the name of a person heading an agency.
When he has one of his executive order-signing events, he just signs whatever is handed to him, then proudly holds up his his signature while stating few words like, "We're building a wall." During interviews, he answers questions in a disjointed way, latching onto one word in his response and allowing that word to point him into a totally different direction, unrelated to the subject at hand.
I don't believe (for the most part) that he's the originator of his stated ideas and policies. He's a shallow-thinking conspiracy theorist, easily influenced and led by those around him. When someone is filming Trump in a room with Steve Brannon, don't watch Trump, watch Brannon. It's quite telling. Brannon acts something like a guy who has spent his life savings collecting expensive, rare model train parts and is delighted to finally get to show off the carefully-constructed train and the village it runs through.
One of the most frightening things about Trump is that he lives in a fantasy world which is also inhabited by some dangerous people.And, he lives in that world as a man void of guiding principles and grounded beliefs.