Aaron Burr was in general disrepute after 1804 because of his political indiscretions and the fatal duel with Hamilton. His soaring ego, however, compelled him to undertake further schemes.
Burr's exact aims are not clear today, but may have involved an effort to capture Spanish possessions in the Southwest or to engineer the secession of western states from the Union, or both. In any event, he worked with two very interesting personalities. One was James Wilkinson, then governor of the Louisiana Territory and a man with a reputation for shady dealing that exceeded even Burrs. The other associate was Harman Blennerhasset, an Irish immigrant who lived in splendor on an island in the Ohio River (near present-day Parkersburg, West Virginia).
In 1806, Blennerhasset provided funding for the outfitting of a small fleet of flatboats; Burrs personal vessel contained all the necessary amenities, including ample wine storage. The assemblage began a cruise down the Ohio River, headed for the Mississippi and eventually for New Orleans. For reasons unknown, Wilkinson reported Burrs actions to President Jefferson. The president ordered Burr's arrest; he was taken to Richmond for trial on charges of treason.
Burrs trial was presided over by none other than John Marshall, Chief Justice of the Supreme Court. (In the early days of the republic Supreme Court justices had little business and spent time on circuit duty.) Marshall, always anxious to spite Jefferson, insisted upon the narrowest possible interpretation of treason, requiring an overt act to prove treason and not just a conspiracy to do so. The case was doomed from the start. Despite Jeffersons stage management, the prosecutions case was badly mishandled and Burr was acquitted.
One significant sidelight of the Burr trial occurred when Chief Justice Marshall subpoenaed Jefferson to testify. The president refused to do so, citing the independent nature of the branches of the government.