Answer: Clement Vallandigham. A former Ohio congressman and the most prominent of the “Copperhead” anti-war Democrats, Vallandigham was court-martialed in 1863 for a speech denouncing “King Lincoln” and the war, and when he was convicted, Lincoln — not wanting to make him a martyr — had him banished to the Confederacy, from where he ran a losing campaign for Ohio governor in absentia. After the war, he returned to a thriving law practice. In 1871, he defended Thomas McGehan, accused of killing Tom Myers in a Hamilton, Ohio, barroom brawl, on the theory that Myers had accidentally shot himself while drawing his own pistol from a kneeling position. Demonstrating the maneuver with a pistol he thought was empty, Vallandigham shot himself in the abdomen and died the next day at 50. The demonstration worked: it convinced the jury, and McGehan was acquitted. Read more here.