James Wilkinson has to rank near the top of this list — many historians actually consider this dude to be America’s greatest scoundrel. Let’s review his career highlights:
Wilkinson served as a Brigadier General in the Revolutionary War. After the war he made his way to the Kentucky Territory and worked a deal with Spain — in exchange for trade concessions with New Orleans, then under Spanish control, he agreed to campaign for Kentucky to become an independent country, to be allied with Spain. For his efforts, he received an annual stipend of $4,000 per year. Wilkinson swore allegiance to Spain and became their secret agent #13. At about the same time, while in the pay of Spain, he was made Commander in Chief of the Army under Jefferson.
During the Lewis and Clark Expedition, Wilkinson informed the Spanish that this force was infringing on Spanish territory, and troops should be sent to capture them. Troops were sent, but they were unsuccessful.
While in charge of the Louisiana Territory, he colluded with Aaron Burr to set up an independent country, comprised of this region and parts of the west under Spanish control. So Wilkinson was now also plotting against Spain, still paying him as a spy. But Wilkinson got cold feet, and so he turned on Burr, who was tried for treason.
Despite evidence of Wilkinson’s involvement, he wasn’t pursued while Jefferson was in office. However, Madison, not being a fan, had Wilkinson court-martialled in 1811 for mismanagement, complicity with Burr, and spying for Spain. Incredibly, Wilkinson was acquitted, albeit just barely, for lack of evidence.