Proverbs 21:2, “Every way of a man is right in his own eyes. This is usually paraphrased as "No man is evil in his own eyes." Just as true, no man likes being seen as evil in other people's eyes.
In WW2, the United States was called upon to fight Nazi Germany and Imperial Japan. Up to this point in Western history, racism was seen as a valid school of thought. In order to muster and unite all the forces of the United States population, the racism of Germany and Japan was portrayed as distinctly evil. This was a great shift in thinking, especially for the last western nation to enslave people based on race. Once something had become evil in men's eyes, there's no way to go back to the old ways.
Over 400,000 US soldiers died in WW2. We need to remember, even though Japan did attack us, neither Germany or Japan were a real threat to the United States. The war was justified on idealistic grounds, not survival. The ideal in this case was the belief that racism is evil.
This directly led to the social upheaval of the 1950's and 1960's in the US. The result was desegregation in schools and public services. It continued with the Civil Rights movement and Lyndon Johnson's Great Society. Whereas the government had been the enforcer of racism in the US, it now became the punisher of racism. There were still plenty of racists. Racism on a practical level is a wide spectrum. It ranges from domestic terrorists such as the KKK, to people who just don't want to live near a black family. These people have a problem, because no one wants to be labeled evil.
The Republican Party was able to corral the residual racism in America by appealing to the fear and resentment held by many white people. The GOP went from being the party of the wealthy and intellectual white upper classes, to the party of the disaffected white working class. This naturally leads to problems, because the rhetoric of racism can't be used in political discourse. This is the core of "political correctness." This leads to a schizophrenia in the Republican Party. They have to deny reality, in order to retain their racist supporters. It becomes a real problem when they are in power, because while the structure of the US government has been transformed and can no longer enforce racism, the GOP has to keep their racists supporters not only mollified, but closeted as well.
That is why President Trump cannot condemn American Nazis.
