In becoming president, then treating it like an extension of his business empire and a chance to advertise his family's products to boot. Did you not see the times he campaigned alongside obviously-placed examples of Trump Merchandise? Do you not notice that he's basing his operations at Trump Tower over or at least equally with the White House (oh and there's another clue to his personality, that and the golden chair that sits in the penthouse of the same)? Do you not hear him talk about himself in the third person? Have you not noticed the pitched battle to get him to sever himself from his business interests? Which he's still struggling to do, it seems, given his tweet about Nordstrom and his daughter's fashion line.
As the Harvard Republican Party put it last year, when it still looked like he might not win: "Trump doesn't plan to solve the US's problems. He plans to exploit them." As you put it, you're being seriously naive.