What I don't quite get about Trump: in what way is he stupider or less marketable than Reagan was? From this far away, there doesn't seem to be a flea fart's difference between them

Reagan was suffering from dementia all thru his presidency - his "cold, dead brain" & all that, so he has a bit of an excuse. Not so his handlers.

Trump? He's just an ignorant imbecile buffoon.

That's the difference.