When is a dress not just a dress? When it could possibly set the political tone for the next four years.

The Smithsonian’s National Museum of American History officially expanded its popular “First Ladies at the Smithsonian” exhibition Wednesday, welcoming first lady Michelle Obama’s dazzling one-shouldered, white-silk chiffon inaugural gown as its new centerpiece. While the Jason Wu-designed dress is the exhibit’s newest piece, there also are about 1,000 other first lady-related treasures, including a dress and dressing mirror once owned by the first first lady, Martha Washington.

But 11 of the inaugural gowns included in the collection have been given special status in their own gallery, “A First Lady’s Debut.” The VIP treatment is certainly deserved: Of all the decisions faced by first ladies, there is perhaps none more closely scrutinized than their inaugural gown pick, which reflects not only the new first lady’s fashion taste but also is seen as a symbol of her husband’s upcoming presidency.

When Obama officially donated her dress on Tuesday, she said she’s “a little embarrassed by all the fuss being made over my dress.” But Obama also recognized her gown’s significance, noting that every inaugural dress, with its unique fabric, cut and color, tells us something about the first lady who wore it.

“Each gown places us right in the moment and makes us wonder about the intimate details of that evening. Like, how did she feel in the dress? Did her feet hurt in those shoes?” Obama joked. “How many times did her husband step on that train?”

Obama’s own gown earned high marks from critics; it was praised for combining romance and glamour with youthfulness and even setting off a one-shoulder dress trend. And by now, most fashionistas (and plenty of D.C. insiders) know the story of Obama’s stunning white gown, which was embellished with organza flowers with Swarovski crystal centers. She combined it with a pair of Jimmy Choo shoes and diamond jewelry designed by Loree Rodkin, which also are on display.

But it was Wu who garnered most of the attention for the ensemble. Wu, age 26 on Inauguration Day, didn’t even know Obama had picked his creation — which he said was intended to symbolize hope — until he saw her wearing it on television. “Frankly, I had no idea I was seriously being considered,” he said.

While Obama’s dress was a well-kept secret prior to the inauguration, some first ladies weren’t able to keep things under wraps before the big night. Descriptions and sketches of now-Secretary of State Hillary Rodham Clinton’s 1993 inaugural gown, a violet beaded piece designed by Arkansas native Sarah Phillips, were printed a week before her husband’s swearing-in.

Clinton’s gown is included in the collection, as are Laura Bush’s ruby-red, crystal-embroidered Chantilly lace dress from President George W. Bush’s 2001 inauguration; her mother-in-law Barbara Bush’s 1989 royal blue gown, with its velvet bodice and asymmetrically draped silk satin skirt that led designer Arnold Scassi to proclaim her “the most glamorous grandmother in the United States”; and Nancy Reagan’s 1981 James Galanos-designed one-shouldered sheath gown of lace over silk satin. (Reagan notably wore the $22,500 gown once more before giving it to the Smithsonian.)

Other inaugural gowns in the collection include pieces from first ladies Rosalynn Carter, Pat Nixon, Betty Ford (her dress is actually from a state dinner, as there were no formal inaugural celebrations when Gerald Ford was sworn in), Lady Bird Johnson, Mamie Eisenhower and Jackie Kennedy, whose off-white sleeveless gown led the Washington Post to report that her “career as a major fashion influence was beginning.”

Several other non-inaugural gowns are included in the first ladies collection, dating back to the country’s beginnings. Along with Washington’s silk taffeta gown from the early 1780s, there are pieces from several first ladies, each reflecting an individual style and the period.

Dolley Madison’s 1810 silk satin open robe, hand-embroidered with flowers, butterflies, dragonflies and phoenixes, is a good representation of the style at the time. Helen Taft’s embroidered Chinese coat, featuring spring and summer symbols of goldfish and lotus flowers, includes fur trim, which likely was added as a custom order, according to the Smithsonian.

And not just fashion is represented in the first ladies collection. There also are treasures from the women’s daily lives, including dishes used for White House entertaining, rare portraits of the women and artifacts that highlight their own interests, including Washington’s sewing case, Christmas cards designed by Kennedy and a small painting by Ellen Wilson.