From Merriam-Webster online
1 : a belief that race is the primary determinant of human traits and capacities and that racial differences produce an inherent superiority of a particular race
2a : a doctrine or political program based on the assumption of racism and designed to execute its principles
b : a political or social system founded on racism
3 : racial prejudice or discrimination
This country's founders, most of its leaders until sometime in the latter half of the 20th century, and much of its white population fit the first definition above. It was the foundation of slavery, the excuse for the displacement and genocide of the indigenous peoples who lived here before the colonizers/oppressors appeared, the basis for Jiim Crow, the founding principle behind the KKK, much of the basis for the political careers of George Wallace, Bull Connor, Jeff Sessions, Roy Moore, and many other Alabama politicians, and an essential part of the Republican party's "southern strategy" which was initiated by Nixon and continued by Reagan, Poppy Bush, and now by #45. Listen to the interview on youtube with Lee Atwater from 1981.
Here's a quote: "You start out in 1954 by saying, “N****r, n****r, n****.” By 1968 you can’t say “n****r”—that hurts you, backfires. So you say stuff like, uh, forced busing, states’ rights, and all that stuff, and you’re getting so abstract. Now, you’re talking about cutting taxes, and all these things you’re talking about are totally economic things and a byproduct of them is, blacks get hurt worse than whites.… “We want to cut this,” is much more abstract than even the busing thing, uh, and a hell of a lot more abstract than “N****, n****r.”
Now, you excuse-makers have two choices: you can recognize the cesspool that Republican politicians have knowingly waded into and helped to perpetuate and pull yourself out and try to clean off the stench, or you can continue making it publicly obvious that your attitudes are accurately described in the first part of the above definition. You can't do both.