Many years ago he very well knew who the KKK was, etc. and suddenly in this election season he plays dumb like he never heard of them.
https://www.factcheck.org/2016/03/trumps-david-duke-amnesia/
never mind this item
Donald Trump's father was arrested at Ku Klux Klan riot in New York in 1927, records reveal
see also "dog whistle" politics
https://en.wikipedia.org/wiki/Dog-whistle_politics
and
Lexicon: The Political “Dog Whistle” Is Obsolete
Nixon used phrases like “law and order” to stir fears of racial conflict without coming right out and saying it. “Race remained the indisputable, intentional subtext of the appeal,” he writes. “As Nixon exulted after watching one of his own commercials: ‘Yep, this hits it right on the nose ... it’s all about law and order and the damn Negro-Puerto Rican groups out there.’”
also
How Trump both stokes and obscures his supporters’ racial resentment
By playing into white fears of crime and concerns that minorities are taking their jobs, he’s signaling to his white supporters that he’s a politician who is finally taking their problems seriously. This is very much racialized (as the latter part of Hochschild’s analogy shows), but Trump does it through dog whistles that somewhat mask the racial element.
But here’s the thing: Many of Trump’s supporters may not even recognize that it’s racial resentment that’s riling them up. In fact, the way Trump and other politicians use coded language allows their supporters to think that these issues have little or nothing to do with race.
“The dog whistle metaphor suggests that the dogs — the intended audience — hear the message clearly. That’s wrong. The code is designed to hide the actual dynamics from the target audience itself,” Ian Haney-López, author of Dog Whistle Politics: How Coded Racial Appeals Have Reinvented Racism and Wrecked the Middle Class, told me. “It’s code designed to allow people who are racially anxious and who are easily fired up with racial narratives to deny to themselves that it’s race that’s agitating them.”
Trump very much knows what he is doing.
That only happened in your mind and is all built around a single comment where Trump said Mexico wasn't sending it's best.