He ran billion dollar business and won primary and presidential elections against all odds. It's time to admit he's not stupid.
It depends on what you classify as stupid. Trump undeniably knows how to work a room, which is fantastic for a politician, but business-wise, Trump made a lot of very costly mistakes decades ago
(as one put it, "how do you lose a billion dollars in the 90s?"), and he has run up a lot of debt. Nonetheless it's still something that he recovered and retooled his business around his personal brand, but I think it would be a mistake to call Trump a well-rounded man. By all accounts, he is not a good businessman. He is a good promoter, which was enough to win a primary and get elected against the 2nd most unpopular candidate in modern history.
As we can see now, he's really an awful politician. He can't control himself, is not strategic and doesn't listen to people. Most of Trump's big issues to date have been self-inflicted wounds, such as firing Comey and then basically stating it was due to the Russia investigation
on live TV. That got Mueller instated and the rest we all know.
So no, while I'd say he has smarts in some areas, he is overall probably an idiot of sorts.