Who is the only US Senator convicted of treason against the US by the Senate? He was also the youngest US Vice President.

John Cabell Breckinridge (born January 16, 1821 – died May 17, 1875) was a lawyer and politician from the U.S. state of Kentucky. He represented the Commonwealth in both houses of Congress and in 1857, became the 14th and youngest-ever (36 years old) Vice President of the United States (1857–61) under President James Buchanan. Later serving in the U.S. Senate at the outbreak of the Civil War, he was expelled after joining the Confederate Army. He remains the only Senator of the United States convicted of treason against the United States of America by the Senate. He was appointed Confederate Secretary of War late in the war. A member of the Breckinridge family, he was the grandson of U.S. Attorney General John Breckinridge, son of Kentucky Secretary of State Cabell Breckinridge and father of Arkansas Congressman Clifton R. Breckinridge.