Heather Cox Richardson is a professor of history at Boston College and the author of “To Make Men Free: A History of the Republican Party.”

For 21 years, Marguerite LeHand was Franklin Delano Roosevelt’s secretary, nurse, cheerleader, adviser and possibly lover. “Missy,” as FDR’s children nicknamed her, was so crucial to FDR’s life and career that he split the income from his estate evenly between her and his wife, Eleanor. But LeHand kept no diary or records, and destroyed her letters. From the time she entered FDR’s service in 1920, her focus was on the man she called “FD.”

Journalist Kathryn Smith’s biography of LeHand presents her as she apparently saw herself: a satellite to the era’s star. Coming into Roosevelt’s circle when a former boss plucked her from government work to join Roosevelt’s staff as he ran for vice president on the 1920 Democratic ticket, LeHand so impressed Eleanor that after the Democrats’ spectacular loss, she asked the young woman to work at the family’s Hyde Park, N.Y., home. From there, LeHand became FDR’s private secretary. She stayed at his side for the next two decades, answering his mail, nursing him through ill health, cheering on his dream of a health resort in rural Georgia. She accompanied FDR on his long rehabilitation vacations in the early 1920s: In the 116 weeks between 1924 and 1928 that FDR was away from his home and family, his mother was with him for two of those weeks, Eleanor for four and LeHand for 110. When FDR was elected governor of New York in 1929, LeHand was at his side, standing on call 24 hours a day for the four years he held that office.

From Albany, LeHand accompanied the Roosevelts to the White House, where she had her own suite and mediated between the president and his wife and children. She worked in a cubbyhole adjoining the Oval Office, where she monitored FDR’s mail and calls and provided private access to the president. Deeply involved in policy discussions, she suggested the appointment of FDR’s attorney general and the nomination of Supreme Court Justice Felix Frankfurter. When Time magazine ran a 1934 story about FDR’s inner circle, LeHand and three men were on the cover. She was the first person in the White House to hear that Germany had invaded Poland, but she would not be at FDR’s side during World War II. A massive stroke in June 1941 incapacitated her until her death in 1944 at age 47.

Was LeHand FDR’s secretary? Lover? Adviser? Who knew? The 1920s ushered in the New Woman who smoked and drank, wore short skirts, and had a career. How did such a woman engage in politics? People tried to fit LeHand into a traditional mold, referring to her as a sort of super-secretary and noting her clothing. “Superficially the most modern of modern women, she actually is like the old-fashioned wife and mother, sacrificing herself on the altar of duty and service,” one reporter wrote. “For her work has taken the place of husband and children and her office is her home.”

"The Gatekeeper: Missy LeHand, FDR, and the Untold Story of the Partnership That Defined a Presidency," by Kathryn Smith E (Touchstone)

This confusion served LeHand well, enabling the child of Irish immigrants to become second only to Eleanor as the most powerful woman in America. That confusion extends less successfully to Smith’s biography. Hampered by LeHand’s own determination to keep the spotlight on FDR, Smith has had to tell LeHand’s story by examining her few extant letters, her charm bracelets and some film clips, and by presenting the era’s larger history, a task at which she excels. Smith has written a highly readable jaunt through some of the nation’s most trying years. She offers a quick and lucid account of Irish immigration, Massachusetts and Georgia history, the Great Crash, and FDR’s New Deal. But the star of the story remains firmly who LeHand wanted it to be: FDR. LeHand’s clothing, love interests and calendar take up more space in her biography than her intellect and power.

But LeHand was a politician above all. While Smith suggests that she avoided marriage because inevitable pregnancies would strain a heart weakened by rheumatic fever, it seems likely that this daughter of immigrants, so extraordinarily talented that she continually caught the eye of superiors, built for herself the only political career open to her. By sitting at FDR’s side, arguing, laughing, cajoling and adoring, she helped to create the New Deal. One observer noted that she was at once “the efficient secretary, the helpful and lively participant in a policy conference, or the gracious hostess at the Roosevelt table.” “Missy,” FDR often said, “is my conscience.” All this from a woman who once told a reporter that she “would hate to be mixed up in politics.”

The New Deal years offered women a political foothold. While Smith tends to dismiss Eleanor Roosevelt as a high-minded harpy whose painful confrontations with FDR were counterproductive, in fact Eleanor was even more central to her husband’s career than LeHand. Eleanor hated the glad-handing of politics, but she made constant social calls to advance FDR’s standing, joined him on the campaign trail and saved his nomination in 1936 by making an appeal directly to the convention. The first lady was the human face of the FDR bureaucracy, winning women and African Americans to the New Deal coalition.

Women first entered government service during the Civil War, and by the time FDR took office they were ubiquitous. Louise Hackmeister ran the White House switchboard; Malvina “Tommy” Thompson was Eleanor’s personal secretary. Legions of other women, making half a man’s salary, performed the backroom duties that kept the government running. Phone calls, letters and access to officials all went through them. Exactly what that meant for government remains obscure, but it is certain they were vital to the structure and substance of American politics. LeHand was more than FDR’s “Girl Friday,” as Smith calls her.

In New Deal America, political women had to define what it meant to be a female politician. LeHand attached herself to a star and stayed in his shadow as she helped change America. Smith’s biography represents her subject perfectly.

The Gatekeeper
Missy LeHand, FDR, and the Untold Story of the Partnership That Defined a Presidency

By Kathryn Smith

Touchstone.
341 pp. $28