Honestly I wouldn't expect Kluxers and normal old world fascists to understand each other. One of them is about race, the other is usually about cultural and ideological divisions. Even if the latter use race as one excuse to murder someone en masse, it's not the core of their ideology, the core is that they should be able and need to practice to murder someone en masse. While American racists are something extremely weird.

"ITS DANKESCHÖN VERDAMMT! YOU ARE BUTCHERING MY BEAUTIFUL LANGUAGE!" - wolfenstein

There was a pro-nazi movement in the U.S. in the 1930's. They had a nazi rally in Madison Square Garden. The nazis went underground for the most part after the U.S. entered WW2.

Very real, as the other comment says. Nazism was big in the US in the yeas before WW2

Many “great” pictures can be found online

It's the 48 Star American flag, thus it's the German American Bund in the 30s. To be fair to the literal Nazis pictured it's before the holocaust was discovered. It's not AI, it appears in this 2017 article: https://www.theatlantic.com/photo/2017/06/american-nazis-in-the-1930sthe-german-american-bund/529185/