Not easy to sum up very succinctly but as an example, it would be reasonable to use the term to describe someone who deliberately ignores cause and effect and who seems not to appreciate that behaving in certain ways brings adverse outcomes.
Taking out of the equation anyone who has learning difficulties, as this does not apply to them, most of us learn that during childhood we cannot always do exactly as we please, we learn that poor behaviour generally has consequences and we learn to understand that building meaningful and co-operative relationships with others is valuable. Stupid people tend not to learn all of these things.
I was thinking cause and effect and generally consequences too when i thought about your earlier post...so i get what you mean. I was acting similarly on many occassions in my life and am happy to admit that i wasn't using my brain properly then.
How this applies to Trump i dunno....difficult to say whats an act, whats a sense of entitlement, whats distraction of other issues, whats hunger for controversy.
To me it is neither here nor there, his politics are at the core of what needs analysing and resisting.
I also don't fully know where to draw the line with terminology....myself, I'm happy to say idiot, but cretin, moron, mongo, etc make me angry when i hear them being used.
I guess the word idiot had long been normalised when i grew up, so carries less clinical baggage in a way....no excuse really, something for me to figure out a bit more.
Lastly, and I'm not nitpicking....people with learning difficulties make mistakes by not connecting cause and effect all the time too. They too have 'stupid moments' and should be allowed to make these mistakes as well as being pulled up on them.
Mileage might vary according to needs and diagnosis of course, allowances can be made.
Everyone is different, no homogenous group, we are all humans etc etc.
Bringing this back to Trump, i think we can be a little bit mindful not to shift the offence we experience when confronted with his way of thinking onto another group of people.