Highest Office Held: President of the United States
Franklin Pierce fell victim to the 1860s-version of hitting "reply all" on an office email. After the Battle of Vicksburg, Confederate President Jefferson Davis's plantation was captured by Union forces. Inside his home were letters between Pierce and Davis revealing their friendship, as well as Pierce's opposition to the war. Just like the time your ex posted those nasty pics of you on Facebook, this did not end well.
Pierce, who already had his share of enemies, was called a traitor by a number of powerful political figures, and faced an angry mob at his doorstep after Lincoln's assassination. Though he eloquently defended himself on the porch of his home after the protesters questioned his allegiance to the USA, the damage had already been done.