How about we've seen the evidence and decided that he's not a smart man, by any measure?
He's bad at everything; he fails at everything except conning idiots. He's consistently lost money all his life. He says stupid things all the time. He can't even come up with smart lies.
And even with his one true skill, conning idiots, he doesn't think it all the way through. Take a look at the recent stories about the "recurring payments" scam he pulled in the last few weeks of the election. It raised well over a hundred million dollars, which by any measure makes it a pretty successful scam.
But of course, Trump didn't think it all the way through. He got to the point where he had the money, but didn't bother to think about 2 major factors: Firstly, the recurring payments in many cases added up to more than the person was legally allowed to donate, so he had to give some of the money back. Secondly, a lot of people, once they realized what had happened, demanded refunds, which Trump also did not think of.
So he had to pull yet another scam, the "Stop the Steal!" fundraising post-election, just to come up with the money he needed to refund all those people. A "successful" con once again, even though it really only succeeded in fixing the screw-ups of the first con.
And consider the situation for the country. Had Trump not needed the millions of dollars from the StS con to fix the earlier con, would he have still be beating that drum months later? Could Trump's screwed-up cons be directly implicated in the attack on the Capitol?
Not being able to see even one iota past the $$$$$ is pretty stupid. Trump is a driver who steered towards a wall, then tried to fix it by steering towards a cliff.