As president, the prime example of his incompetence was the embargo, which totally failed in its foreign policy objectives, ruined our own economy because implementing it required halting our coastal domestic transport, and required a more intrusive government than anything the British tried in colonial times to enforce the Navigation Acts.
The irony is, of course, that Jefferson (the planter) suffered greatly from Jefferson's (the President) decision to impose the embargo.
Probably only because he had to pay higher prices for his French wine.