This is where we see things entirely differently.  You envision a change of form as a change of content.  I don't.  US social, political, economic, legal and educational institutions are inherently white-supremacist and always have been--and very much with us today.  I can provide quotes from prominent white Americans--including most presidents--from the 18th century to now, and including "notables" from Benjamin Franklin to Henry Kissinger and beyond, which openly admit this.

Nor was white supremacy always legally codified--there were seldom statutes allowing lynching even in the Jim Crow south.  But thousands of people were lynched nonetheless, with "officers of the law" usually leading the mob.  I eschew the term "racism" as inaccurate, and for having been misappropriated by (usually white) apologists for American white supremacy, and thus having been deprived of any real meaning.

(2) Nor by allowing it to persist unchallenged.
(3) You didn't really answer this one.  Try again.