In September 1863, the Ohio politician John Bingham was at the lowest point of his career. He had once been among the fastest-rising stars in American politics. Nine years earlier, he was among the first group of Republicans elected to the House of Representatives. Shortly after arriving in Washington, he established himself as one of the leading congressional voices against slavery. He was one of the new President Lincoln’s most steadfast supporters and a key member of the House’s pro-war caucus.

But things soon turned difficult. Bingham’s Ohio district was redrawn after the 1860 census. Meanwhile, support for the war was flagging in the North, and soldiers at the front were not allowed to vote with absentee ballots. As a result, Bingham was drummed out of Congress during the 1862 elections.

Despite this personal and professional setback, Bingham remained confident about his future and of Union victory. The political views he espoused in Congress, he believed, would triumph; though currently unpopular, they would return to public favor in time – and with them, his own career. He told Treasury Secretary Salmon P. Chase that the “limitations of the Constitution upon the States in favor of the personal liberty of all of the citizens of Republic black & white [are] soon to become a great question before the people.”...