The U.S. anti-Communist crackdowns are remembered disapprovingly as "Red Scares". The use of similar methods against Nazi supporters during the Second World War is rarely described as a "Brown Scare". Why?
This is an extremely well-researched and detailed article. I was surprised you did not mention the role of the British Security Corporation, an undercover British propaganda operation. Among other things, it worked to discredit isolationist congressmen including Hamilton Fish. The existence of the BSC was revealed in 1997, with the publication of Nigel West Ed.
British Security Corporation: The Secret History of British Intelligence in the Americas 1940-1945.h
George Sylvester Viereck was a German propagandist in WWI. Am reasonably certain that Fritz Duquesne and Elsbeth Schragmüller were the principal inspirations for the spy couple in the 1969 classic 'Fräulein Doktor.' Then there is Fritz von Pappen, the ridiculous WWI German spymaster in the US who became Hitler's vice chancellor. There are enough links between the two German influence campaigns ("German Scares"?) that a clever historian could write a single book about them both.