John Henry Eaton (June 18, 1790November 17, 1856) was an American politician and ambassador from Tennessee who served as U.S. Senator and as U.S. Secretary of War in the administration of Andrew Jackson. He was 28 years, 4 months, and 29 days old when he entered the Senate, making him the youngest U.S. Senator in history.

Eaton was a lawyer in Tennessee who became part of a network that supported the political campaigns of Andrew Jackson. He also served in the militia as a major, and during the War of 1812 became an aide to Jackson; Eaton served with Jackson in all his wartime campaigns and battles, including the Battle of New Orleans. After serving in the Tennessee House of Representatives in 1815 and 1816, in 1818 Eaton was elected to the U.S. Senate, though he had not yet reached the constitutionally mandated age of 30.

Following Jackson's election to the presidency in 1828, Eaton resigned his Senate seat to join Jackson's cabinet as Secretary of War. Eaton and his wife Peggy became the focus of controversy during Jackson's first term; in the so-called Petticoat affair, Washington's society wives refused to socialize with the Eatons. The wives of the vice president, cabinet members, and members of Congress looked down on Peggy because of the circumstances of her marriage to Eaton; they had wed shortly after the death of her first husband, without waiting for the usual mourning period, giving rise to rumors that she had been unfaithful to her first husband before his death. Eaton resigned as Secretary of War as part of a strategy to resolve the controversy; he later received appointments as Governor of Florida Territory and U.S. Minister to Spain.

Upon returning to the United States in 1840, Eaton refused to endorse incumbent Martin Van Buren for reelection to the presidency, angering Jackson. In retirement, Eaton resided in Washington. He died there in 1856, and was buried at Oak Hill Cemetery.

Early life John Eaton was born on June 18, 1790, near Scotland Neck, Halifax County, North Carolina to John and Elizabeth Eaton. The elder John Eaton was a furniture maker who served as county coroner and member of the North Carolina House of Representatives. Eaton's uncle, Major Pinketham Eaton (sometimes spelled Pinkerton), was a Continental Army officer who died in combat during the Revolutionary War. The first Eaton forebear in America was Andrew Eaton, a watchmaker from Godalming, Surrey born in 1678 who emigrated to North Carolina in 1699. Eaton's father owned a large amount of land in middle Tennessee, and the 1790 census lists him as the owner of 12 slaves. The younger Eaton attended the University of North Carolina at Chapel Hill from 1802 to 1804. He then studied law, attained admission to the bar, and moved to Franklin, Tennessee, where he established a law practice. He apparently became a slave owner, as in 1813 he placed a runaway slave ad seeking the recovery of a teenager named Abraham. Abraham had a stutter and had crossed the Cumberland River near Haysborough and was thought to have procured a free pass.

Eaton became active in the Tennessee militia, and attained the rank of major. He developed a close friendship with Andrew Jackson, and served as an aide to Jackson during the Creek War and the War of 1812. Eaton took part in all Jackson's major campaigns. He supported Jackson's controversial decision in November 1814 to attack Pensacola in Spanish Florida, claiming that Spain had put herself in a belligerent position by allowing its territory to be occupied by British soldiers. Eaton participated in the Battle of New Orleans. After the war, Jackson took command of the Southern U.S. Army District with his headquarters at his home, The Hermitage. Eaton served on his staff. Eaton later became a major proponent of Jackson's presidential candidacy. He also wrote the epitaph on Rachel Jackson's grave.

John Reid, another Jackson aide, began a biography of Jackson in 1816, but died after writing only four chapters. Eaton finished the book, which was published as The Life of Andrew Jackson in 1817. This book was revised and republished in 1824 and 1828 to coincide with Jackson's presidential campaigns. It became a major primary reference for future Jackson biographers.

Senate career From 1815 to 1816, Eaton was a member of the Tennessee House of Representatives. In 1818, he was elected to serve as a U.S. Senator from Tennessee, and he served until 1829. His age of 28 at the time of his entry to the Senate was notable; it violated the U.S. Constitution's requirement that all senators be at least 30 years old. Eaton's age of 28 makes him the youngest person ever known to have served in the Senate.

Eaton was a slaveowner, but, unlike many Southerners, he supported the Missouri Compromise of 1820. On March 11, 1820, in a letter to Jackson, he claimed that "it has preserved piece and dissipated angry feelings, and dispelled appearances which seemed dark and horrible and threatening to the interest and harmony of the nation." He remained a close friend of Jackson, and while in the Senate supported the Jacksonian movement. He urged Jackson to accept an appointment as Governor of the newly acquired Florida Territory in 1821, which he did. From 1827 to 1829, Eaton served as Chairman of the Senate Committee on the District of Columbia.

In 1822, Eaton and his brother-in-law William Berkeley Lewis attempted to nominate a candidate before the Tennessee legislature to oppose incumbent U.S. Senator John Williams, who was openly against Jackson's candidacy for president in 1824 presidential election. After being unable to find a viable candidate, they nominated Jackson himself. The strategy was successful, and Jackson won. Eaton also helped advance Jackson's campaign for president through the Letters of Wyoming, which were printed in newspapers. In them, Eaton praised Jackson's record. He celebrated even some of Jackson's most controversial actions, such as the suspension of habeas corpus in New Orleans in 1815. "Washington would have done the same," he asserted. An anti-Jacksonian of Louisiana, Samuel Clement, wrote in 1827 that Eaton "by most impartial persons is considered as the General's mouth-piece, or amanuensis..."

In 1825, Eaton received an honorary degree (Master of Arts) from the University of North Carolina. Eaton supported the Tariff of 1828, or the "Tariff of Abominations."

Marriages In 1813, Eaton married his first wife, Myra Lewis (1788–1815), the daughter of William Terrell Lewis, a prominent Tennessee businessman and landowner. After the death of their father, Jackson became legal guardian to Myra and her sister Mary, and Eaton's marriage to Myra Lewis strengthened his relationship with Jackson.

Eaton married his second wife Peggy O'Neill Timberlake (1799–1879) in 1829, while serving in the Senate. She was the mother of three children; a son William, who died as an infant, and daughters Virginia and Margaret. Eaton had been a longtime friend of Peggy Timberlake and her husband John B. Timberlake, and John Timberlake had died only a few months before Eaton married his widow. Jackson knew and liked Peggy Eaton and encouraged Eaton to marry her, telling him "Why yes, Major. If you love the woman, and she will have you, marry her by all means." He asked Eaton to marry her as soon as possible. Eaton had no children with either wife.

Secretary of War Petticoat affair

Jackson, leading the new Democratic Party, won the 1828 presidential election, and in March 1829 Eaton resigned his Senate seat to accept appointment as Jackson's Secretary of War. The appointment was seemingly made because of Jackson's desire to have a personal friend in the Cabinet in whom he could confide.

Women in Washington social circles led by Floride Calhoun, the wife of Vice President John C. Calhoun, snubbed the Eatons because they married so soon after John Timberlake's death, rather than waiting for the usual mourning period; there were stories that Eaton and Peggy Timberlake had been having an affair before John Timberlake had died. Rumors held that Peggy, as a barmaid in her father's tavern, had been sexually promiscuous or had even been a prostitute. Petticoat politics emerged when the wives of cabinet members, led by Mrs. Calhoun, refused to socialize with the Eatons. They refused to attend social events at which she would be present. According to Emily Donelson, Eaton considered resigning in the first months of the administration.

Jackson refused to believe the rumors about Mrs. Eaton's past conduct, telling his Cabinet that "She is as chaste as a virgin!" In his view, the dishonorable people were the rumormongers, in part because he was reminded of the attacks that had been made, particularly in the 1828 election, against his wife over the circumstances of their marriage. Jackson also believed that John Calhoun fanned the flames of the controversy as a way to gain political leverage for a growing anti-Jackson coalition. Duff Green, a Calhoun protégé and editor of the United States Telegraph, accused Eaton of secretly working to have pro-Calhoun cabinet members Samuel D. Ingham (Treasury) and John Branch (Navy) removed from their positions.

Jackson biographers Richard B. Latner and Robert V. Remini believe that the hostility towards the Eatons was rooted less in questions of morality and proper behavior than in politics. Eaton had been in favor of the Tariff of Abominations, which Calhoun bitterly opposed and which led him to elucidate the doctrine of nullification. He was also close to Secretary of State Martin Van Buren, another supporter of the tariff and Calhoun's main rival for who would succeed Jackson as president. Calhoun may have wanted to expel Eaton from the cabinet as a way of boosting his anti-tariff agenda and increasing his standing in the Democratic Party. Many other cabinet members were Southerners and may have felt similarly, especially Ingham, a close Calhoun ally who supported his presidential aspirations.

Eaton took his revenge on Calhoun. In the spring of 1830, reports emerged accurately stating that Calhoun, while Secretary of War, had favored censuring Jackson for his 1818 invasion of Florida. These infuriated Jackson. The biggest bombshell was a letter given to Jackson on May 12 by William H. Crawford, Monroe's Secretary of the Treasury, in which Crawford stated that, contrary to Jackson's former suspicions, it was Calhoun, not himself, who vocally advocated censuring Jackson in Monroe's cabinet. For reasons unclear, Calhoun asked Eaton to approach Jackson about the possibility of Calhoun publishing his correspondence with Jackson at the time of the Seminole War. Eaton did nothing. This caused Calhoun to believe that Jackson had approved the publication of the letters. Calhoun published them in the Telegraph. This gave the appearance of Calhoun trying to justify himself against a conspiracy to damage him, and further enraged the President.

Meanwhile, Van Buren, a widower, took Jackson's side and defended the Eatons. This raised Van Buren in Jackson's esteem, and, in addition to disagreements between Jackson and Calhoun on a number of other issues, mainly the Nullification Crisis, marked him as Calhoun's likely vice presidential successor. In the spring of 1831, Van Buren helped end the Petticoat affair by offering to resign as Secretary of State. This gave Jackson the opportunity to reorganize his cabinet by asking for other resignations, and he was able to replace the anti-Eaton secretaries; only Postmaster General William T. Barry remained. Eaton, being the source of the controversy, also agreed to resign his position.