When James Buchanan became the first bachelor President, various rumors circulated in Washington society about the unusual situation. One tale told the story of a youthful Buchanan who had vowed never to marry when a misunderstanding with his fiancée caused her suicide. Another more persistent account cited Buchanan's longtime relationship with the also unmarried Senator William Rufus Devane King from Alabama. The two had lived together in Washington for sixteen years, and letters between them indicate that Buchanan and King had, at the very least, shared a deep friendship. In any event, Buchanan was without a wife but not at a loss for female companionship. He surrounded himself with the wives of his friends and political advisers and contented himself with the company of his ward and niece, Harriet Lane. "Nunc," as Harriet referred to him, had educated his niece about the importance of politics, discussing political issues with her. When James Buchanan became President, he asked Harriet to assume the duties of presidential hostess.

The role did not intimidate the twenty-seven-year-old. When her uncle served as ambassador to Britain, Harriet experienced life at the British court and became a favorite of Queen Victoria. During James Buchanan's 1856 campaign for the presidency, Harriet hosted events which helped promote his bid for office. Thus, when Harriet entered the White House, she took up her duties with great confidence. Although she pursued no one special project, Harriet used her position to draw attention to the fine arts. She invited artists to her events and began to lobby for a national art gallery. Interest in art spurred another passion. During her time in England, Harriet began to study, collect, and promote Native American arts at a time when the arts of Africa and Asia were generating interest in the West. Her appreciation of indigenous artistic expression led to her tolerance of minorities in general and to her interest in the welfare of Native Americans in particular. She worked with reformers to educate lawmakers about the medical and educational needs of the various tribes and tried to stop the sale of liquor on the reservations. Because of her efforts, the Chippewa Nation heralded her as the "Great Mother of the Indians."If Harriet Lane was a "Great Mother" to some, she was a "Democratic Queen" to many others. After four years of the sad and dour Jane Pierce, Americans were ready for a vivacious social leader. Harriet Lane did not disappoint them. Her inaugural gown marked her as a fashion icon, and her penchant for carrying bouquets of roses and vacationing at exclusive spas made her a glamorous figure. Her youth and beauty captivated an American public which named flowers, perfumes, poems, and clothing for her, treating her as American royalty. But some soon wondered if their "Democratic Queen" would actually become Queen of England. In 1860, Edward Albert, the Prince of Wales, paid a visit to the United States. His trip was followed closely by the press, which noted that the couple toured Mount Vernon, danced together, and played games of tenpins. But even as Harriet entertained English royalty, she was more than a social hostess for her uncle; she was in many ways James Buchanan's partner. He clearly appreciated Harriet's role and accorded her all the prestige enjoyed by a presidential spouse. Despite the pair's closeness, the relationship at times grew strained. Harriet never appreciated having to entertain suitors with "Nunc" looking on, and she resented him opening her mail. Her discontent was evident when, in 1859, she took a three-month summer vacation from the capital and the President.

Despite their differences, Harriet remained an important source of support for her uncle during the sectional crisis. Like most Americans, Harriet had been aware of the increasing tensions in the country. It appears that she privately opposed slavery and Southern secession, though she worried about the country's economic future if the "peculiar institution" were abolished. Publicly, however, she remained silent on the issue of slavery and insisted that her guests follow her example. Her social skills began to serve a political purpose as she manipulated complex seating arrangements at dinner parties and entertainments, keeping political foes apart and dispensing equal favor to all. Unfortunately, her efforts at keeping the peace at White House social gatherings translated neither into a smooth presidency for her uncle nor into peace for the nation. Indeed, the commencement of the Civil War and Abraham Lincoln's valiant and successful struggle to save the Union, as well as the shrewishness of Mary Todd Lincoln, have eclipsed both the presidency of James Buchanan and the tenure of Harriet Lane.