I think Trump is a retard. I've said many times I have yet to meet or encounter a con artist who was not dumber than a bag of dildoes.
I estimate Trump's IQ to be around 80 to 85.
I have no doubt Trump believed the Ukraine/Crowdstrike hoax. He's stupid enough.
As for trying to extort Zelensky, Trump knew exactly what he was doing. I explained in
How The Trump Con Works the methods he uses to pull off his tricks.
You can see the same con at work in the Mueller report. Several times, Trump dictated to people around him exactly what lies he wanted them to say in public. He dictated in private to Comey, Sessions, and McGahn exactly what to say, so he could later point to their words in public as proof he was innocent. He tried to force them to lie so he could point to their statements and their standing to get himself off the hook with the rubes.
Fortunately, these honorable men refused to play along.
Trump actually put his lies in writing that he wanted these men to say.
If they had, Trump would be more than impeachable. Even the Republican Senate would have had no choice but to boot his ass to the curb.