He's probably of above-average intelligence (but not super-smart like a few of the Presidents), just lazy and ignorant, because he has had things handed to him all his life without having to put much effort into it. He sees the Presidency as alternating between playing golf and making campaign speeches. Any real work is left to others.
Don’t forget he’s also a pretty boy with a big smile which is another reason he gets his arse kissed and is able to scam people so much.