You're shitting me. Bush was stupid, Reagan was pretty dumb, Ford was not a bright light, but NOBODY beats the orange moron in stupidity. EVERY world leader and bureaucrat who met him said they couldn't believe how stupid he really was.
NATO had to condense talking points to 15 sec blurbs or the idiot would tune out. He had to pay someone to take his entrance exam, he wouldn't release his "grades". He couldn't talk without trying to read from large print cheat cards. He said and tweeted moronic stupidity after moronic stupidity every day for 4 years. That's the "connection" between him and his cult followers: the dumb and retarded see their own image reflected in that stupid, asinine, fat mug. 
You make some very good points.
Re: Trump I was putting too much emphasis on his ability to string words and sentences together and speak for a long period of time
without stumbling rather than considering the stuff you cited.
Also the fact that he appealed to QAnons, most of whom are not very bright, is an indication that Trump himself is not bright.
When Bush spoke , I just got an overall feeling listening to him that what he said and how he said it was not very Presidential.
I still wonder to this day how the fuck Bush graduated from Yale.
I still also remember very well the dumb expression on his face on 9/11 speaking to school kids when notified that we had been attacked.
"Perhaps" h was able to graduate because "money talks."
That said, I would take Bush or any of the guys you cited over Trump, the big reason being that unlike Trump, these folks
were not 100% self-centered and had empathy for people, although admittedly imo Bush to some extent was controlled by big money interests.
When you come down to it,r e: the Presidency imo pure intelligence and how much one has pales in comparison to what one is a person,
and imo in that regard Trump comes in dead last with no one even remotely close!
There is no reason to delineate the reasons because they are all well known.
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