An email brings a link to a radio program at the BBC on an attempted coup during the Roosevelt presidency:

The Whitehouse Coup, BBC: Document uncovers details of a planned coup in the USA in 1933 by right-wing American businessmen The coup was aimed at toppling President Franklin D Roosevelt with the help of half-a-million war veterans. The plotters, who were alleged to involve some of the most famous families in America, (owners of Heinz, Birds Eye, Goodtea, Maxwell Hse & George Bush’s Grandfather, Prescott) believed that their country should adopt the policies of Hitler and Mussolini to beat the great depression. Mike Thomson investigates why so little is known about this biggest ever peacetime threat to American democracy. [Listen to this programme in full] [View a picture gallery of images related to this edition]

I'm not overly familiar with this episode, so here's what Wikipedia has to say: