It would be senseless for Hitler to throw German resources into support for a fringe movement like the Klan of the late 1930's--let alone to endorse obviously futile and suicidal violence by such a movement, which when German involvement was discovered would simply make US war against Germany more likely. He wanted to get existing governments and major parties to adopt Germany-friendly policies. Discreet cultivation of isolationist Republicans and Democrats was one thing; backing the Klan, let alone insurrection, was another. Even in the case of German-Americans, the regime eventually tried to distance itself from the German American Bund:
"Kuhn and a few other
Bundmen traveled to
Berlin to attend the
1936 Summer Olympics. During the trip, he visited the
Reich Chancellery, where his picture was taken with
Hitler.
[6] This act did not constitute an official Nazi approval for Kuhn's organization: German Ambassador to the United States
Hans-Heinrich Dieckhoff expressed his disapproval and concern over the group to Berlin, causing distrust between the Bund and the Nazi regime.
[6] The organization received no financial or verbal support from Germany. In response to the outrage of Jewish war veterans, Congress in 1938 passed the
Foreign Agents Registration Act requiring foreign agents to register with the State Department. On March 1, 1938, the Nazi government decreed that no
Reichsdeutsche [German nationals] could be a member of the Bund, and that no Nazi emblems were to be used by the organization.
[6] This was done both to appease the U.S. and to distance Germany from the Bund, which was increasingly a cause of embarrassment with its rhetoric and actions.
[6]"
https://en.wikipedia.org/wiki/German_American_Bund
Indeed, even in nations where Nazi-like movements were far stronger than in the US, and where Hitler was in a position to help them, he preferred to work with existing pro-German "conservative" governments, putting
Realpolitik over ideology. As John Lukacs notes in
The Hitler of History:
"All over Europe (for example, in Holland, Denmark, France, Romania, and in a few remarkable instances even in Austria), local National Socialist leaders were abashed when they found that Hitler did not support them and paid them hardly any interest at all. He preferred to work with the established pro-German governments of such provinces and states. The most telling example of this occurred in Romania in January 1941. There the National Socialist and populist Iron Guard (whose anti-Semitic ideology and practices were perhaps the most fanatic and radical in all Europe) got into conflict with the nationalist and military government of General Antonescu, whom Hitler respected and liked. When in January 1941 fighting broke out between the Antonescu and Iron Guard forces, the Germans unequivocally supported the former at the expense of the latter, on occasion with German armor and tanks.
"Of course he had his reasons. While the war lasted, he needed order in the countries that were his allies or satellites--a kind of stability that must not be endangered by revolutionary experiments, and that assured undisrupted deliveries of necessary material supplies to the Reich. Thus he put up for a long time with allied chiefs of state—a Petain, an Antonescu, Regent Horthy of Hungary, King Boris of Bulgaria—some of whom he knew were not wholly loyal or unconditional adherents of a National Socialist Germany. Still, it is significant that he did not offer the slightest promise or give the slightest indication to the effect that sooner or later, perhaps after the war, his foreign National Socialist followers would get their rewards.* [FN] He would, of course, recognize and support some of them in 1944, when his former satellites or junior parmers deserted him; but that was no longer important."
https://books.google.com/books?id=oRwJs6qCMvIC&pg=PA162#