In 1933 Major General Smedley Butler proclaimed there was a Coup d'état plot against Roosevelt by the Fascist American upper class who were opposed to the New Deal.
He was asked to lead half a million men to take the white house and establish a dictatorship. The excuse for the coup was going to be that the president's health was failing. Of course, this was just to mask the true reasons.
Specifically, conservative businessmen saw the items of the new deal as a step towards communism. A big thing they hated was that the New Deal would mark the end of the Gold Standard for currency.
Butler, being patriotic, declined the offer and blew the whistle on the plot. Although a special committee that investigated it found that Butler's allegations were likely true, no one was ever prosecuted for it.