As the term came into more common use, candidate Trump picked it up and began using it as way to dismiss news coverage he didn't like. That is, he effectively changed the meaning of the term from "news parody" to "legitimate news that's false." Except that the news reports he was calling false weren't false. He just didn't like them.
This did a lot of Impact. Trump saying that the news he didn't like was "fake news" allowed the term to be used by lots of people when they didn't like the argument that was presented against them.