Daniel Sickles won a seat in the United States House of Representatives in 1856, representing a district in New York City. He was re-elected in 1858, and served from 1857 to 1861.

Sickles did not seek a third term in Congress in the election of 1860, having just been the subject of one of the most salacious murder trials in the history of the nation’s capital.

On Feb. 27, 1859, Congressman Sickles shot numerous times an unarmed man named Philip Barton Key who died later that day.

Key, who was from a prominent family and was serving as the United States attorney in Washington, was openly having...