Michelle Obama at a rally for Barack Obama in Londonderry, New Hampshire, October 2007. Photograph by Brigitte Lacombe.

As Michelle Obama strolls around Mack’s Apples Pick-Your-Own orchard greeting people at the Londonderry children’s fair, she seems relaxed and friendly, her casual manner belying the pressing schedule that just whisked her from Chicago to New Hampshire and will soon rush her off to an afternoon packed with other events.

But when she addresses the crowd, there is no mistaking her sense of urgency as she makes an impassioned case for her husband’s presidential candidacy. “I am desperate for change—now,” she says, “not in 8 years or 12 years, but right now. We don’t have time to wait. We need big change—not just the shifting of power among insiders. We need to change the game, because the game is broken. When I think about the country I want to give my children, it’s not the world we have now. All I have to do is look into the faces of my children, and I realize how much work we need to do.”

Right now the Obamas’ daughters, six-year-old Sasha and nine-year-old Malia, are bouncing on the inflated castle at the fair, oblivious to the country’s problems. But for some of the assembled voters, their father’s youth is also an issue. Even his admirers acknowledge that, at 46, Barack Obama—a first-term senator and the youngest presidential contender in either party—has great potential but is relatively green. Most of his rivals are over 60, and many analysts have viewed the 2008 campaign as an exploratory run that could set the groundwork for a future race when Obama is more seasoned and the electorate has adjusted to the idea of America’s first black president.

Michelle Obama, who turns 44 in mid-January, is also young, by First Lady standards. Regally tall, stunning, and city-chic in a triple strand of pearls atop her country-casual pants-and-sweater outfit, she manages to look as down to earth as any other soccer mom and as glamorous as a model while instantly commanding respect, even before she starts to speak.

But Mrs. Obama has no interest in an ongoing quest for the White House. “To me, it’s now or never,” she tells me a few days later, in Chicago, where we’ve met up again at the campaign’s Michigan Avenue headquarters. “We’re not going to keep running and running and running, because at some point you do get the life beaten out of you. It hasn’t been beaten out of us yet. We need to be in there now, while we’re still fresh and open and fearless and bold. You lose some of that over time. Barack is not cautious yet; he’s ready to change the world, and we need that. So if we’re going to be cautious, I’d rather let somebody else do it, because that’s a big investment of time, just to do it the same way. There’s an inconvenience factor there, and if we’re going to uproot our lives, then let’s hopefully make a real big dent in what it means to be president of the United States.”

And what it means to Mrs. Obama is sacrificing many of the things she holds most dear, in favor of a larger goal. Although she has concluded that this mission is worth what it takes, achieving such acceptance has been difficult, and the adjustments are ongoing.

Her husband’s vaulting ambition was always a given. “She knew what she was getting into,” says Craig Robinson, Michelle’s brother, who is the men’s basketball head coach at Brown University. “Ever since I’ve known Barack, he’s said that he wanted to be in politics. He’s never changed his interests; it just happened that he’s turned out to be very good at it.”

But Obama’s accelerated timetable came as a shock, even to his spouse. As recently as 2000, Obama—then a little-known Illinois state senator—lost his first race for Congress. But in 2004 he ran for the U.S. Senate and won in a landslide victory, collecting more votes than any Illinois politician in history and becoming the nation’s only black senator.

No sooner had his family adjusted to that development than he started to consider a run for the presidency in 2008. “This was a sudden decision,” Mrs. Obama says. “He had just won his U.S. Senate seat. In my mind, it was ‘O.K., here we are—you’re a U.S. senator.’ ”

With Barack commuting to Washington while Michelle and the children remained in Chicago, the family’s life was already complicated, and Michelle was stunned when Barack abruptly fast-forwarded his presidential aspirations. “I thought, Uhhhh—you’re kidding! It was like, No, not right now—right? There was a period of ‘Let’s not do this now; let’s press the “easy” button! Can we get a break, please?’ ”

She sighs and rolls her eyes. “So we had to talk about it. Before I signed on, I had to know, in my mind and my heart, how is this going to work for me, and would I be O.K. with that? He wouldn’t have done this if he didn’t feel confident that I felt good about it, because it is a huge sacrifice. The pressure and stress on the family isn’t new. But we entered this thing knowing it was going to be really, really hard. For us, the question was: are we ready to do something really hard again, right after doing something that was really hard?”

Barack eventually managed to persuade the whole family that his quest justified the cost. “This is something that’s bigger than everybody,” says Craig Robinson. “This is so important that it’s worth her saying, ‘I’ve got to rethink the way my family is structured.’ ”

Although Mrs. Obama had recently been appointed as vice president at the University of Chicago Medical Center, her husband’s announcement in February 2007 that he was entering the presidential race forced her to scale back her professional commitments. In May, she reduced her work schedule to 20 percent in order to meet the needs of her family while participating in the campaign.

“She was intending to take a full leave of absence, but she couldn’t make herself separate from this professional career that’s been so important to her,” says Susan Sher, vice president for legal and governmental affairs at the University of Chicago Medical Center, where she is Mrs. Obama’s boss. “Her involvement in her work life has been so serious that it’s not easy to just say, ‘Never mind.’ ”

Mrs. Obama has a long history of speaking out about the ways in which men’s choices—particularly their professional ambitions—often leave their wives to pick up the slack, even when they have their own careers. “What I notice about men, all men, is that their order is me, my family, God is in there somewhere, but me is first,” she told the Chicago Tribune in 2004. “And for women, me is fourth, and that’s not healthy.”

But for the moment, at least, Mrs. Obama has reconciled herself to putting her career on the back burner. “The way I look at it is, We’re running for president of the United States. Me, Barack, Sasha, Malia, my mom, my brother, his sisters—we’re all running,” she says. “I can’t hold down a full-time job as vice president of community and external affairs and be on the road three or four days a week. Barack has never asked me to stop doing my job; as far as he was concerned, ‘You have to do whatever makes you feel comfortable.’ But, for me, it was: How can I not be part of this? How can I go to work every day, when we’re trying to do something I believe in? If I really felt it was more important for me to be vice president of community and external affairs full-time, I would do that. But the bigger goal here is to get a good president—somebody I believe in, like Barack, who’s really going to be focused on the needs of ordinary people. For what I’m trying to do at the hospital, getting him elected is a better way for me to reach that goal. Part of doing this is that I would have felt guilty not doing it. I would have felt I was being selfish. We have this opportunity, and Barack could do amazing things, but I wanted help with the laundry? Now my conscience is clear.”

That equanimity has been hard-won, however. Earlier in their 15-year marriage, she was often furious with her husband. “I have chosen a life with a ridiculous schedule, a life that requires me to be gone from Michelle and the girls for long stretches of time and that exposes Michelle to all sorts of stress,” Barack wrote in his best-seller The Audacity of Hope. By the time their second child was born, he reported, “my wife’s anger toward me seemed barely contained. ‘You only think of yourself,’ she would tell me. ‘I never thought I’d have to raise a family alone.’ ”

Mrs. Obama finally got tired of being enraged and miserable. “One day I woke up and said, ‘I can’t live my life mad. This is just no fun,’ ” she reports. “For a period in my life, I thought the help I needed had to come from Barack. It wasn’t that he didn’t care, but he wasn’t there. So I enlisted moms and babysitters and got help with the housecleaning, and I built that community myself.”

She also had to re-evaluate the gap between her own expectations and her husband’s far more flexible ideas about family life. “I came into our marriage with a more traditional notion of what a family is,” she says. “It was what I knew growing up—the mother at home, the father works, you have dinner around the table. I had a very stable, conventional upbringing, and that felt very safe to me. And then I married a man who came from a very different kind of upbringing. He didn’t grow up with a father; his mother traveled the world. So we both came to this marriage with very different notions about what children need, and what does a couple need to be happy.”

She shrugs resignedly. “So I had to give up some of my notions, and so did he. That’s part of being married; everyone makes compromises. Once I got a sense that the family we were creating was going to be good for our children, I realized that it wasn’t exactly what I had, but our children are thriving and they feel loved. Part of my fear was: Are my kids going to be O.K.? If they don’t see their dad at night, like I did, will they feel he loves them? Barack grew up not seeing his mother for months at a time. There was a period when his mother stayed in Indonesia and he came back to Hawaii, and he was living with his grandparents. And he experienced that fully feeling that ‘my mother loves me deeply.’ So he was more comfortable with those choices than I was, and that was an adjustment that I had to make.”

It was one of many. A graduate of Princeton University and Harvard Law School, Michelle Robinson met her future spouse when she was assigned to mentor him at the Chicago law firm of Sidley Austin; although he is three years older, he was still a law student at the time. In 1992 Michelle decided to leave the law firm and pursue a career in public service. “She just knew the private practice of law was not sufficiently satisfying, and she was willing to walk away from a huge salary potential and all the trappings of power that go along with it,” says Valerie Jarrett, a longtime friend and former boss.

But even before Michelle married Barack, she was consulting him about her career decisions. Jarrett was Chicago mayor Richard M. Daley’s deputy chief of staff when she first met Michelle and offered her a job—whereupon Michelle asked Jarrett to meet with her and Barack to discuss his reservations about the offer.

“He had some trepidation about her going to the mayor’s office and joining the Daley administration,” says Jarrett, who is now president and C.E.O. of the Habitat Company, a real-estate development-and-management company. Although she admits it was highly irregular for a job-seeker to request that a prospective boss meet with her fiancé, Jarrett says, “I think it’s a sign of a real partnership, that they are friends and advisers who think through major decisions together.”

One clue to Michelle’s approach may lie in her relationship with her older brother, which was both close and competitive. As a high-school junior, she visited Craig at Princeton University, which had recruited him to play basketball. “I’m smarter than he is,” she thought, and determined to attend Princeton herself—which she did.

Even as a child, however, Michelle had figured out how to wield power over an older, larger sibling while appearing to defer to him. “We had this game where we set up two rooms and played ‘Office,’ ” says her brother, who grew up to be six feet six inches tall. “She was the secretary, and I was the boss. But she did everything. It was her game, and I kind of had nothing to do.”

Her daughters are a major reason Mrs. Obama has tried to avoid that dynamic with her husband. “When he comes home, he’s taking out the garbage and he’s doing the laundry and he’s making up the beds, because the girls need to see him doing that, and he knows I need him to do that,” she says.

She grins, her eyes twinkling. “And that was a meeting of the minds that we had to reach. I wasn’t content with saying, ‘You’re doing important things in the world, so go off and be important and I’ll handle everything else here’—because the truth is, if I did that, I’d probably still be angry.”

Their friends say that both Obamas have made significant sacrifices to accommodate each other’s needs. “Sometimes one person compromises and sometimes the other one does,” says Cindy Moelis, a former colleague of Michelle’s in the Chicago mayor’s office who is currently executive director of the Pritzker Traubert Family Foundation. Money worries were one issue, according to Moelis: “They had a lot of student loans, and there was a lot of tension around that. Barack’s choices made her life harder.” When Barack wrote a book that became a best-seller, the resulting income eased the Obamas’ financial situation. Another example Moelis cites is Michelle’s decision to stay in Chicago after Barack became a U.S. senator. “People said, ‘He needs you in Washington,’ but her friends and family and support system are here, and she said, ‘This is where I’m going to be,’ ” Moelis reports.

Mrs. Obama does not affect the kind of pious deference favored by many other political wives. On the campaign trail, she takes pains not to exaggerate her husband’s admittedly stellar qualities, and she has often startled observers with her sardonic sense of humor—including her admonition that her husband is “just a man.”

Many voters are delighted by a degree of candor they find appealing and reassuring. “When Michelle Obama talks about Senator Obama, she makes you laugh, because he puts his dirty towels on the floor like any other husband,” says Brenda MacLellan, co-chairman of New Hampshire’s Henniker Democrats. “She talks with the dignity of a First Lady, but you don’t have to be prim and proper to be First Lady. She’s a real person, and we need real people in Washington. I don’t want any more surprises. We can’t afford any more surprises.”

But others are put off by Mrs. Obama’s tart-tongued irreverence, and some of her comments have attracted disproportionate attention. The media pounced on such innocuous remarks as Mrs. Obama’s admission that her husband can be “snore-y and stinky” in the morning, as well as her wry complaint that Barack once rushed out of the house and left her to deal with an overflowing toilet.

When I ask Mrs. Obama if she is censoring herself these days, she gives me a rueful smile. “I’m kind of sarcastic, and I’ve felt that my sense of humor had to be subjugated on some level,” she admits. “My husband loves my sense of humor, and we tease each other mercilessly. But if somebody doesn’t get the joke, then you become a caricature of what the joke was. So it’s like, Well, jeez—let me not joke, then, if it’s going to be all that problematic. People get real worked up about some things I felt were really minor, funny, harmless observations about who we are as people.”

Mrs. Obama nonetheless believes that it’s better for voters to understand her husband and herself before deciding on their choice. “My hope is that Americans really want to know who the people who are going to be in the White House are,” she says. “What’s our sense of humor? What are we trying to accomplish? What are our values? My view is: know that now; make the judgment. I think people are ready for truth, if it’s real—so that’s what I’m banking on.”

In any case, the American electorate won’t be treated to any displays of the adoring-spouse pose perfected by Nancy Reagan, who never tweaked her husband in public and whose worshipful mask never slipped no matter how many times she sat through the same speech. “I can’t do that,” Mrs. Obama says. “That’s not me. I love my husband. I think he’s one of the most brilliant men I’ve ever met, and he knows that. But he’s not perfect, and I don’t want the world to want him to be perfect. If you look for that, then people can’t try hard stuff, because you might mess up. We want leaders to be bold and to try some things that might not work, because they might work and be great. I think that’s one of our failings as a nation—we’re looking for our leaders to be something that’s not realistic, and then we’re deeply disappointed when they don’t live up to those unrealistic standards. So let’s shake that up a little bit. We’re moving into the 21st century, and life is different. We’ve struggled; we’ve grown. Let’s not be hypocrites about it, either. Let’s not say we want one thing and then demand you be something you’re not.”

Some voters contrast the Obamas’ apparent openness with the hairsplitting evasions that alienated many of the Clintons’ former admirers. “I trust Michelle to tell you how it is, good or bad,” says one longtime Democratic activist at an Obama event in New Hampshire. “But I don’t trust Hillary to tell me the truth, and I don’t want to deal with all the history of Bill’s infidelity. Why didn’t she kick his ass out? I know many women who would be voting for her if she had kicked him out.” She scowls, and then confides that her own unfaithful husband left her with two children and another on the way. “I don’t need Hillary’s baggage,” she says. “I’ve got enough of my own.”

The Clintons have long elicited such intensely personal reactions, and their marriage continues to occupy center stage despite decades of public scrutiny. Some voters see the Obamas as representing the chance for a fresh start with honest straight shooters—a prospect that Mrs. Obama deftly encourages. “Barack will not be a perfect president, but he will always tell you the truth,” Mrs. Obama assures her audience in Londonderry. “You will always know where he stands.”

Though she never mentions the Clintons, her emphasis on her husband’s personal integrity implies a clear contrast between the Clintons’ oft-tortured marriage and her own. Her husband has behaved honorably in his personal as well as his political life, she says: “He is a fabulous husband and father, and I think that is right up there with everything else you should look at.”

Some of her husband’s supporters give Mrs. Obama much of the credit. “She talks about Barack being a good husband, but it takes a strong wife to make a good husband,” says Representative Paul Hodes, a New Hampshire Democrat who has endorsed Obama.

So far Mrs. Obama has avoided making any specific promises about what she would do as First Lady. But as for who she would be, her attitude is clear: what you see is what you get.

“I am really being as authentically me as I can be,” she says. “When people ask, ‘What kind of First Lady will you be?’—I’m going to try, in all this, to be honest, hopefully funny, and open, and share important parts of me with people, hopefully in a way that will help them think about their lives and avoid the mistakes we may have made in our lifetime. What you see on the trail is probably who I will be as First Lady, because that’s really who I am.”

But she has no illusions about maintaining an independent career if her husband reaches the White House. “Absolutely not,” she says. “I don’t think that’s possible or realistic or desirable. Everything I do on my job would pose some huge conflict.”

These days her very participation in the current campaign reflects the depth of her commitment to her husband’s goal, according to her friends. “She hasn’t taken this role every time he’s run for office,” says Cindy Moelis. “This is the first time in all these elections that I’ve seen her be as passionate and committed as she has been.”

“I think they really struggled through it, but once the decision was made, she’s totally gung-ho,” says Susan Sher.

As for the outcome of this race, Mrs. Obama seems philosophical about her husband’s prospects. “We’re doing our best,” she says. “I hand it over to people and say, ‘O.K.—it’s on you,’ so I’m good.”

Such earnestness proves too much of a temptation, however, and she quickly succumbs to a characteristic flash of mischievous humor. “I’m good,” she repeats, her voice starting to quaver. “No, really—really! Can’t you tell? I’m great with it!” She buries her head in her hands and pretends to sob.

But then she straightens up in her chair and gives a blank, faux-happy smile, as if beaming mindlessly for the camera. Nobody’s perfect, and Michelle Obama—lawyer, soccer mom, hospital executive, Senate wife, potential First Lady—is the last person who would ever want you to think she considers herself a finished product who has it all together.

“I think I’m 60 percent there,” she says. “I’m still a work in progress, too.”

Leslie Bennetts is a Vanity Fair contributing editor.