On the evening of March 21, 1864, the quiet of a small corner of the Army of the Potomac’s sprawling winter camp along the Rappahannock River near Beverly Ford, Va., was disturbed when a fight broke out in one of the mess tents between Union Army civilian employees Moses J. Robinette and John J. Alexander.

The scuffle left Alexander bleeding from knife wounds, and Robinette was charged with attempted murder and incarcerated on a remote island near modern-day Florida. It would also cause an unexpected intersection in the histories of two American presidents, Lincoln and Biden — a story that has waited 160 years to be told.

Robinette, who received a pardon from Lincoln, was Biden’s great-great-grandfather.

Joseph Robinette Biden’s ancestral line has long been established and lists Moses J. Robinette among his paternal ancestors hailing from western Maryland, but very little has ever been chronicled about the man. Robinette’s court-martial records, discovered at the National Archives in Washington, show how the current president’s story is intertwined with that of the man who was president at the most perilous junction in U.S. history.

In 1861, Robinette was 42, married and running a hotel near the Baltimore and Ohio Railroad junction at Grafton, Va. Union sentiments ran high in Virginia’s mountainous western counties, which soon broke off to form the new state of West Virginia. As the nation lurched toward armed conflict that spring, smoldering resentments against Virginia’s politically dominant slaveholding elite flared into open defiance after northwestern delegates tried to block the secession movement and were expelled from the Virginia Convention.

Western Virginia became an early battleground as both sides fought to control the railroad. Union troops occupied Grafton in mid-June 1861 and drove Confederate forces out of the region within six months. The Robinette family suffered setbacks in the war’s early years: Moses’s wife, Jane, died, and his hotel was destroyed, allegedly by Union soldiers. Seeking safety for his youngest surviving children, Robinette appears to have left Virginia and returned to his extended family in Allegany County, Md.

Robinette was hired as a civilian veterinary surgeon by the U.S. Army Quartermaster’s Department in late 1862 or early 1863. He was assigned to the Army of the Potomac’s reserve artillery and tasked with keeping healthy the horses and mules that pulled the ammunition wagons. His qualifications for the position, as someone without formal medical training, were unstated, but such an appointment was not unusual in Civil War armies. Few veterinary colleges existed outside Europe in the 19th century, and Congress refused to authorize the creation of an official army veterinary corps until the First World War.

On that March evening near Beverly Ford, Alexander, a brigade wagon master, overheard Robinette saying something about him to the female cook and rushed into the mess shanty to demand an explanation. Tempers flared, expletives followed, and Robinette drew his pocketknife. A brief scuffle left Alexander bleeding from several cuts before camp watchmen arrived to arrest Robinette.

Nearly a month passed before Robinette’s military trial began. The charges specified that he had become intoxicated and incited “a dangerous quarrel,” violating good order and military discipline. Because a drawn weapon was involved, assault with “attempt to kill” was included among the charges.

Witnesses described Robinette as “full of fun, always lively and joking,” and testimony varied on whether either man had consumed alcohol before the fight broke out.

According to the trial transcript, Robinette stated in closing “that whatever I have done was done in self defence, that I had no malice towards Mr. Alexander before or since. He grabbed me and possibly might have injured me seriously had I not resorted to the means that I did.”

The military judges were not convinced. The next day, they rendered a unanimous verdict: guilty on all counts with the exception of “attempt to kill.” The punishment was two years’ incarceration at hard labor.

After his conviction, Robinette again had to wait nearly three months for his case to churn through the army’s bureaucratic channels. Occupied by active military operations, the commander of the Army of the Potomac, Gen. George G. Meade, did not confirm Robinette’s sentence until early July, when he was sent to the Dry Tortugas islands near Key West, Fla.

The islands were home to Fort Jefferson, a giant brick structure designed to protect the southern coast and Gulf of Mexico shipping lanes. The massive increase in U.S. forces needed to fight the Civil War correspondingly ballooned the number of military trials and convictions. When mainland prison space ran short, Fort Jefferson became a military prison, one described by Lincoln’s opponents as “American Siberia.” When Robinette disembarked there, the growing prison population numbered more than 700.

Around the time Robinette arrived on Dry Tortugas, three army officers who knew him petitioned Lincoln to overturn his conviction. John S. Burdett, David L. Smith and Samuel R. Steel wrote that Robinette’s sentence was unduly harsh for “defending himself and cutting with a Penknife a Teamster much his superior in strength and Size, all under the impulse of the excitement of the moment.”

They testified that Robinette had, from the outbreak of the war, been “ardent, and Influential … in opposing Traitors and their schemes to destroy the Government.”

The letter concluded with an emotional flourish: “Think of his motherless Daughters and sons at home! … [Praying for] your interposition in behalf of the unfortunate Father … and distressed family of loved Children, Union Daughters & Union Sons.”

The missive did not go straight to the White House, but first landed on the desk of Waitman T. Willey, a newly elected senator from the recently admitted state of West Virginia. He endorsed the plea, calling Robinette’s punishment “a hard sentence on the case as stated.” Lincoln’s private secretary, John G. Nicolay, promptly requested that the judge advocate general, Joseph Holt, send over a report and the trial transcripts for presidential review.

Holt’s report arrived in late August, and Lincoln made his decision, writing, “Pardon for unexecuted part of punishment. A. Lincoln. Sep. 1. 1864.” Shortly thereafter, the War Department issued Special Orders No. 296, freeing Robinette from prison.

After more than a month on sweltering Dry Tortugas, Robinette returned to his family in Maryland, where he took up farming again. He lived into the 20th century, dying at his daughter’s home in 1903. While his brief obituary eulogized him as a “man of education and gentlemanly attainments,” no mention was made of his wartime court-martial or his fleeting connection to Abraham Lincoln.

But the slender sheaf of 22 well-preserved pages of his trial transcript, unobtrusively squeezed among many hundreds of other routine court-martial cases in the National Archives, reveals the hidden link between the two men — and between two presidents across the centuries. Those few pages not only fill in an unknown piece of Biden family history, but also serve as a reminder of just how many Civil War stories have yet to be told.

David J. Gerleman is a 19th-century historian, Lincoln scholar and history instructor at George Mason University in Fairfax, Va.