This argument is, in a word, nonsense.
The political pundit class (and the journalists that may in their wake) may be well aware of Trump’s character flaws and shadiness, but I would suggest that most Trump voters know him as (to quote Timothy Snyder), “Donald Trump, Successful Businessman.” They know the character he played on The Apprentice, and the guy on the cover of The Art Of the Deal.
What they do not know is that he is a crook, a cheapskate, and a business failure several times over. That is the story that the current investigations and lawsuits against him will tell, and it is one that voters need to hear over and over.
So please, let’s retire this faux-savvy notion that “Everyone already knows this.”