The concept of "race" does not reflect empirical reality as it actually exists.
Racism and white supremacy are based on a concept which is a "true lie" that dominant society makes real, both for those who benefit from racial inequality as well as those who suffer under it.
In all, Charles Blow's sharp observation that, "This is at the core: White extinction anxiety, white displacement anxiety, white minority anxiety. This is the fear and anxiety Trump is playing to" actually brings up something deeper, more existential and in many ways more sinister both because of the collective psychology involved and what such a conclusion then mandates as a necessary and reasonable response to an existential threat.
Best I can parse this article is its demonstrating how a shift in ideas from "We're white people, and we're cool" to "We're white people, and maybe that doesn't make us that cool." (And the guilt looking back on what people did in the name of being cool) Which, in turn, leads to the 'existential threat' from "What if we're just people."
Then again, I guess I just summed up the growing pains of the Civil Rights movement from the 'white peoples'' side.