However, one of Roosevelt's first acts was to eliminate the gold standard. That so angered the bankers that they began to pursue a coup. They hoped to use veterans who had been promised money, but the payments had been delayed. These veterans would violently depose Roosevelt. Congress conducted investigations, but the insurrectionists were too important, and the whole thing was whitewashed.

Per Wikipedia on The Business Plot : "Retired Marine Corps Major General Smedley Butler asserted that wealthy businessmen were plotting to create a fascist veterans' organization with Butler as its leader and use it in a coup d'état to overthrow Roosevelt. In 1934, Butler testified under oath before the United States House of Representatives Special Committee on Un-American Activities (the "McCormack–Dickstein Committee" ) on these revelations."

[en.wikipedia.org]

So we don't have to go all the way back to the Civil War to find an analogy to Jan 6. "In July 2007, Scott Horton wrote an article in Harper's Magazine claiming that Prescott Bush, father of US President George H. W. Bush and grandfather of then-president George W. Bush, was to have been a "key liaison" between the 1933 Business Plotters and the newly emerged Nazi regime in Germany."