While Klan, pro-Nazi and other anti- Semitic,racist activities have been a minor inconvenience occasionally popping up in the background for the past 30 or so years, it was not till Charlottesville that a sitting POTUS openly praised adherents of those ideologies as "good people". Trump also retweeted numerous "pro-fascist",anti semitic memes that a little research shows appearing on fascist twitter pages a few days prior to being slightly modified and retweeted by Trump. I can speak from firsthand knowledge here, because when the controversy over the Star of David Tweet first broke, I was able to go back and find the Neo-Nazi twitter site where the image/ad originally came from.
https://www.cnn.com/2016/07/04/politics/donald-trump-star-of-david-tweet-explained/index.html
Even more blatant was his embrace of the Charlottesville thugs, which included James Fields the murderer of Heather Heyer. Fields is a member of Vanguard, a pro-Nazi/Fascist organization whose original website Blood and Soil, was inspired by the SS slogan Blut und Boden. Prior to their hosting being shut down I visited their site, and on it they proudly proclaimed themselves the New American Fascists.Fields himself can be seen in videos marching with his tiki torch bros on the Fri night prior to the murder,yelling "Jews will not replace us" outside the main Synagogue in Charlottesville during Fri night services. It was a scene right out of Kristallnacht and Trump's failure to unequivocally denounce those forces is just one of many examples of why he is not qualified to serve as POTUS.