In 1934 Smedley Butler, a highly decorated US Marine, told the US Congress that a group of industrialists wanted him to lead a coup to put the US back on the gold standard and reverse the New Deal--the Business Plot.
This has been discussed on this sub before here with an answer by /u/InfamousBrad, who says:
What we'll never know: if Butler made it all up (a popular opinion), or if the American Legion guy did make the offer but was deluded about having the money and the soldiers to offer Butler (my personal opinion) or if there really was a credible coup plot (not a popular opinion).
Is "Butler made it up" really the usual opinion among historians? What could his motive possibly have been?
The whole situation strikes me as bizarre. Butler was pro-Roosevelt and did not have a business-friendly reputation. This makes his story implausible on its face; if he made it up, why did he expect others to believe him? If it's all MacGuire's doing, what was in it for MacGuire?
In my experience, the Business Plot is one of those events where there are just enough sources and reports around to allow people to see what they want to see.
In "The Plot to Seize the White House: The Shocking True Story of the Conspiracy to Overthrow FDR", Jules Archer writes from the perspective that Butler's testimony and inferences about the plot are 100% correct. This work builds on the work of George Seldes and John L. Spivak, who originally reported on the conspiracy, and it's also the one that is loved most by conspiracy theorists (which is why the text of the book can be found on a conspiracy theory website here) and people who take the plot at 100% face value. When I read it, it was clear that the book was not written to be evenhanded - it was written as muckracking history.
This tends to match criticisms of the book: James Sargent's 1974 review concludes that "Archer’s Plot should be compared to well-researches and comprehensive studies on related subjects, like George Wolfskill, The Revolt of the Conservatives (1962), Wolfskill and John A. Hudson, All But the People (1969) and Walter Goodman, The Committee (1968). Because of its flaws, I would not recommend Archer’s book for either upper-level of graduate courses on American history, and its too lengthy and slanted for survey courses."
In a thesis by Emily Lacy Marshall, it's noted that Archer's one of the few that has written directly and with a primary focus on the plot - other historians have touched on it but not focused on it. Her thesis does, and from what I've read so far, it's a much more evenhanded treatment of the plot (which is like saying it's less slanted than the Daily Mail), though I haven't gotten to finish it.