The advertisements for ABC’s new drama “Commander in Chief” state its premise clearly: “This fall, a woman will be president.” Political types may see the show as a focus group on the public’s comfort with a Hillary campaign, but inquiring minds want to know: What on earth would a female president wear?

Tonight, when “Commander in Chief” premieres, viewers will get a look at a fictional answer to that question. The central character is Mackenzie Allen – played by Geena Davis – who was elected vice president but takes the top job after the sitting president dies. She succeeds him even though his dying wish (echoed by her political party) is that she will step aside.

For costume designer Mimi Melgaard, this plot wrinkle had a lot to do with creating the look for Ms. Davis’s character. “Mackenzie Allen comes in and tries to follow her heart in the job,” said Ms. Melgaard, who developed a key thought that guided her choices for the character. “She doesn’t have to give up her femininity for power.”

To introduce President Allen, Ms. Melgaard stuck to suits that are tailored and conservative. “I used a lot of Armani, especially in the first five episodes, because I wanted to keep it serious,” she said. “We wanted it to be believable.”

Of supreme importance were dark colors and excellent tailoring. Though the colors are dark at first, they will lighten during the season. In addition to Giorgio Armani, Ms. Davis will wear suits by Gucci, Ralph Lauren, and Oscar de la Renta. Silk blouses with soft collars by Dolce & Gabbana are also in the wardrobe. “I searched every designer for everything. I didn’t use anyone exclusively,” the costumer said.

But the suits aren’t exactly off-the-rack: Ms. Melgaard sent them down to the costume department’s shop and had them tailored to fit the star. “I re-cut almost everything. Everything was completely fit to her,” Ms. Melgaard said. “Geena has such a beautiful body, so you can see the curves.”

Can the public handle a curvy commander? Women who have actually run for the White House, served in Congress, or even just been around politics, know that the reality is thorny. Pat Schroeder, who considered a run for president in 1987 and is now the president and CEO of the Association of American Publishers, remembers the pitfalls well. “Visuals are so important,” she said. “For men, it’s so easy. There’s a whole formula: red tie, blue suit. To be casual, they roll up the sleeves. Women either look too stiff or too informal.”

During the days in which Ms. Schroeder explored a race for the presidency, she observed that though the public was eager for a change, they were reluctant to break the mold. “People would say, in the same sentence, ‘They all look the same, but you don’t look presidential,'” she said.

Before running, Ms. Schroeder spent 12 terms in Congress, where she found the constant critique of her dress frustrating. “I would have people sending me checks, telling me to dye to my hair. I bet Al Gore didn’t get notes like that,” she said.

But Ms. Schroeder stuck to the uniform. “I was always in suits. I used to have a dream of retiring, digging a big hole, and putting all my suits in it,” she said.

She did make exceptions, such as in a group photo of all the female elected officials (“There were, like, 14 of us.”) on the Hill. But it wasn’t a good move, she found, when the critical letters started coming in. “‘You’re the only one not in a suit. You wore a dress,'” she said, paraphrasing the notes.

For the fictional president on “Commander in Chief,” there is less of a rigid code. Viewers will see this president working out in rowing gear, getting ready for bed in her pajamas (tank top by C & C of California and silk pants by Donna Karan), and attending a formal state dinner.

Creating the right formal gown turned out to be the toughest part of the costuming process. “To have a president in a strapless gown, is that appropriate? We spent weeks and weeks on this,” Ms. Melgaard said, adding that there is very little skin showing. “She is covered below her knees. There is no cleavage, and she wears gloves.”

The idea of the strapless gown was approved – a decision based on the rationale that the character has to do things her own way. But after that, the right one had to be found. “It was Los Angeles in the summer, and we could not find a gown,” said Ms. Melgaard. “Geena came up with the idea of looking at wedding dresses.”

The savior turned out to be the wedding dress manufacturer Amsale. Though they usually make all-white dresses, the company kicked into high gear and made a navyblue dress in less than two weeks. “They ended up custom-making the dress and custom-dying the beads. They hand-dyed the beads,” Ms. Melgaard said. “The dress looks like a million bucks.”

While a fictional character can be as glamorous, strapless, and fashionable as she likes, a real-life female president would face much more trouble, accord ing to Georgette Mosbacher, a GOP fundraiser and president and CEO of Borghese cosmetics. “Any woman who is smart enough to get to the presidency will have learned. She’s going to keep it noncontroversial,” she said. “We still live in a time when if a woman is going to be taken seriously, she has to dress like a man.”

Former congresswoman and vice-presidential candidate Geraldine Ferraro disagrees. “Look at Secretary of State Condoleezza Rice. Nobody doubts she’s smart as hell,” she said. “Madeleine Albright was always extremely stylish. Olympia Snowe always looked as if she walked out of Vogue.”

Ms. Ferraro does acknowledge that women have to think about not distracting from their message with their dress, which is not something that their male colleagues bother with. “Men don’t have to think about that,” she said.

Former British prime minister Margaret Thatcher managed to strike a balance that kept the attention squarely on politics. “Her clothes were very tailored. She wore a basic suit, with lining to match, and a basic blouse. For evening, it was a skirt to the floor, and the lining in satin,” Ms. Mosbacher said, pointing out that Mrs. Thatcher’s dress evolved. “She went from dowdy house dresses to that suit. You can practically see the day she said to someone, ‘Make me over as the prime minister.'”

As for pants, the PM just didn’t consider them. Ms. Mosbacher recalls a walk on the beach with Mrs. Thatcher, who wore pumps and a skirt for the outing. “She told me she never owned a pair of slacks,” Ms. Mosbacher said.

In “Commander in Chief,” pants are allowed. Allen wears a pair of khakis in a casual scene. But what is also allowed is having all the characters look sharp. For research, Ms. Melgaard looked at scores of photos of press conferences, congressional leaders, first ladies, and, of course, Secretary of State Condoleezza Rice. “One of the things we’re trying to do is make it look a little bit nicer than it really is,” said Ms. Melgaard.

She applied that rule to the reporters – “We didn’t want to make a statement about them looking shabby.” And to the city’s characters as a whole: “I’ve seen the guys in Congress,” she said. “Some of them have had those suits for 15 years.”