The full extent of the plot is unclear, but that there was some kind of plot is certain. Many financial and business leaders of the time were rumored to be fascists like Lindbergh.[1]
Of course, if you compare Butler's handler to the strange cast of characters in the history of widely-known American political plots (Watergate, Iran-Contra, etc.), truth is often stranger than fiction.
[1] William Dodd, the U.S. Ambassador to Germany, in a letter to FDR (from the same link above):
"A clique of U.S. industrialists is hell-bent to bring a fascist state to supplant our democratic government and is working closely with the fascist regime in Germany and Italy. I have had plenty of opportunity in my post in Berlin to witness how close some of our American ruling families are to the Nazi regime. ... A prominent executive of one of the largest corporations, told me point blank that he would be ready to take definite action to bring fascism into America if President Roosevelt continued his progressive policies. Certain American industrialists had a great deal to do with bringing fascist regimes into being in both Germany and Italy. They extended aid to help Fascism occupy the seat of power, and they are helping to keep it there. Propagandists for fascist groups try to dismiss the fascist scare. We should be aware of the symptoms. When industrialists ignore laws designed for social and economic progress they will seek recourse to a fascist state when the institutions of our government compel them to comply with the provisions."
Lindbergh was not a fascist; he was an isolationist.
His stated strategy to the coming war was that Hitler would eventually turn on Russia (he was right) and that Germany and Russia would grind each other down (also true: the total destruction of the Sixth Army at Stalingrad (now Volgograd) is one example).
After both countries were very weak, then American armies could swoop in and mop up after both armies had exhausted themselves, with minimal losses to the American side.
Of course, if you compare Butler's handler to the strange cast of characters in the history of widely-known American political plots (Watergate, Iran-Contra, etc.), truth is often stranger than fiction.
[1] William Dodd, the U.S. Ambassador to Germany, in a letter to FDR (from the same link above):
"A clique of U.S. industrialists is hell-bent to bring a fascist state to supplant our democratic government and is working closely with the fascist regime in Germany and Italy. I have had plenty of opportunity in my post in Berlin to witness how close some of our American ruling families are to the Nazi regime. ... A prominent executive of one of the largest corporations, told me point blank that he would be ready to take definite action to bring fascism into America if President Roosevelt continued his progressive policies. Certain American industrialists had a great deal to do with bringing fascist regimes into being in both Germany and Italy. They extended aid to help Fascism occupy the seat of power, and they are helping to keep it there. Propagandists for fascist groups try to dismiss the fascist scare. We should be aware of the symptoms. When industrialists ignore laws designed for social and economic progress they will seek recourse to a fascist state when the institutions of our government compel them to comply with the provisions."