The Union Army of the Potomac was a hotbed of political activity during the Civil War. It proved a source of constant frustration for Abraham Lincoln, and its commander, George B. McClellan, even secured the Democratic nomination for president in 1864. This book uses untapped sources to recast our understanding of soldier ideology and presents the most comprehensive view yet of the army’s political story. It recounts the struggle between Republicans and Democrats for political allegiance among the army’s rank and file, in the process showing that the army’s captains, majors, and colonels spurred a pro-Republican political awakening among the enlisted men that burst onto the public stage through newspaper editorials, unit resolutions, and letters to home front politicians. The book traces the heated campaigning and voting activity on the front lines during critical elections such as the 1864 presidential contest, highlighting how an army that had once revered McClellan renounced him for consorting with the forces of peace activism and treason. Union soldiers asserted themselves as the guardians of civic virtue and used the power of political organization to set the terms in a heated debate over wartime loyalty.