Who is the only president to commit a public act of treason against the U.S. Government?

As president in the early 1840s, Tyler, who is a native Virginian, supported many policies his party did not including states rights and slavery. Sixteen years after leaving office, when the Civil War seemed inevitable, Tyler embraces the Confederacy and urged fellow Virginians to join him. He was eventually elected to the Confederate Congress, which was officially at war with the country he once served.