How did Trump's term for news reports that criticize with him come to be used to describe serious propaganda and disinformation efforts?
You've got the timeline backwards. It was a legitimate term used to describe political disinformation which was coopted by Trump and his supporters.
It's sticky, it's simple, it's basic. Ref and I are no longer speaking over the definition of "feedback" and I'd wager 90% of the country couldn't define "propaganda" with a gun to their head. In an earlier era, "news" was "information of value." Then we got "news feeds" and they were basically "a bunch of shit you have to filter through." "fake news" is that shit in your facebook feed you can slag on the poster for sharing while "propaganda" is something the Nazis did. Maybe. They did have a few good ideas. And were such snappy dressers. Unlike Shillary. Pantsuits I swear to christ...