CHICAGO — There is no confusing Michelle Obama for her husband on the campaign trail.
Asked at the Democratic debate in Los Angeles whether he would pick Senator Hillary Rodham Clinton as a vice-presidential running mate, Senator Barack Obama said she “would be on anybody’s short list.”
But when a television interviewer asked Mrs. Obama last week whether she would support Mrs. Clinton, if she won the nomination, Mrs. Obama was less generous.
“I’d have to think about that,” Mrs. Obama said on “Good Morning America” on ABC. “I’d have to think about — policies, her approach, her tone.”
Outspoken, strong-willed, funny, gutsy and sometimes sarcastic, Michelle Obama is playing a pivotal role in her husband’s campaign as it builds on a series of successes, including a sweep on Tuesday of contests in Maryland, Virginia and the District of Columbia.
Her personal style — forthright, comfortable in the trenches, and often more blunt than Mr. Obama — plays well with a broad swath of the electorate and has given the campaign a steelier edge while allowing Mr. Obama to stay largely above it all.
“I am trying to be as authentically me as I can be,” Mrs. Obama said in an interview. “My statements are coming from my experiences and my observations and my frustrations.”
Mrs. Obama says she dislikes politics — she insists there will be no second run for the presidency if her husband falls short this time — but relishes a good fight, the competition of it all.
In the beginning, she had significant questions about an Obama candidacy. She pressed advisers for a blueprint of how the campaign would raise money and compete with Mrs. Clinton and other candidates. She gave her approval after seeing a concrete plan presented in strategy meetings in late 2006, all of which she attended.
Now she is involved in most major facets of campaign strategy, always a fierce protector of her husband’s image. While the Obamas seldom travel together — fanning out much as the Clintons do — Mrs. Obama is often in touch with key advisers and her message is shaped by the same strategists who advise her husband.
“The strategy is not to pigeonhole her to any one kind of audience,” said Valerie Jarrett, a close family friend who is a senior adviser to the Obama campaign.
Growing up in Chicago, her brother, Craig Robinson, recalls, Mrs. Obama did not like watching close basketball games, but would always watch blowouts to the end.
“She didn’t like the stress of watching,” said Mr. Robinson, the men’s basketball coach at Brown University. Thinking about the campaign for a moment, he added: “It’s much harder watching Barack in this race than watching my own team. It’s much harder to watch someone you love go through a close game.”
At almost six feet tall in heels, Mrs. Obama, 44, cuts an athletic and authoritative figure in her tailored pantsuits and skirts. A Harvard-educated lawyer who had been earning $212,000 a year as a hospital executive before she took leave on Jan. 1, she delivers rousing 40-minute speeches — surveying topics as far-ranging as the specific failings of the federal No Child Left Behind education act and problems with the military strategy in Iraq — without the aid of even a notecard.
A doting mother of two, Mrs. Obama has kept crowds waiting with telephone calls to her “little people” — daughters Sasha, 6, and Malia, 9.
But Mrs. Obama’s confident, commanding presence has its drawbacks. At an address last month for an African-American awards gala in Atlanta, some in attendance were left feeling that she had been condescending, preaching to a group of achievers about the need to achieve.
“Her speech was very long and inappropriate for that occasion,” said Vivian Creighton Bishop, a public official in Columbus, Ga., who supports Mrs. Clinton.
Mrs. Obama has also had to learn to tamp down her sometimes biting humor because it too often leaves Mr. Obama as the punch line. (It has been a long time since she has talked publicly about her husband of 15 years being smelly in the morning, as she told Glamour magazine, or forgetting to put away the butter.)
“What I’ve learned is that my humor doesn’t translate to print all the time,” she said in the interview. “But usually when I’m speaking to a group, people understand what I’m trying to say, they get the humor, they understand the sarcasm, they get the joke.”
Her audiences do laugh. Talking about how long it took her and Mr. Obama, 46, to pay off their student loans (they did so only in the last couple of years), she told a church audience in Cheraw, S.C., “I’m still waiting for Barack’s trust fund.” They cackled. She continued: “Then I heard Dick Cheney was supposed to be a relative! Thought we might be in for something here.”
On some occasions, Mrs. Obama’s straight talk has also made it necessary for the campaign to explain her remarks. In the case of “Good Morning America,” campaign officials pointed out that in an unbroadcast portion of the interview, Mrs. Obama later acknowledged that as a good Democrat, she would need to support Mrs. Clinton if she were the nominee.
Mrs. Obama’s nickname inside the campaign is “the closer” because she is skilled at persuading undecided voters to sign pledge cards. But as a smooth orator, she is also known as a connector, volunteering her own life lessons from working-class roots and discussing her confrontation with a culture of low expectations.
She has been transparent about more mundane things, too, like leaning on her mother for child care while she is on the road.
Mrs. Obama does not have a nanny, only her mother. “Thank God for Grandma!” Mrs. Obama says more than once on the campaign trail, adding that she “couldn’t breathe” if she thought her girls, who attend private school here in Chicago, were being neglected for the campaign.
“I spend more time worrying about how do I keep their lives on track in the midst of this?” she said in the interview. “Barack and I both do. How do we keep our traditions whole? Those are the day-to-day concerns.”
In a presidential campaign that has included discussions of race and gender, Mrs. Obama has a singular vantage point at the intersection of the two. As the advantage in some states has seesawed between Mr. Obama, of Illinois, and Mrs. Clinton, of New York, based in part on the votes of blacks and women, Mrs. Obama typically makes a plea for unity, even when race- or gender-based appeals might be expedient and easy.
That was the case when they packed the pews to hear her one Friday night last month in a modest Methodist church in Orangeburg, S.C.
“Oh, amen!” the participants cried out over the rise and fall of her voice, springing to their feet, howling their approval with hands lifted as if in praise.
It was the eve of the Democratic primary in South Carolina, and Mrs. Obama was urging the audience to the polls. But they were urging her on, too: “Come on now, tell it, sister!”
And so she did, focusing on the economic hardships facing many Americans: “What we have to understand in this race is that this is true regardless of the color of your skin, regardless of your gender,” she said to the mostly black audience. “This is the truth of living in America.”
Interviews with people who know Mrs. Obama say she chose, even as a young adult, to strive for the opportunities that were closed to previous generations.
Mrs. Obama grew up knowing, for instance, that her maternal grandfather, a carpenter, was squeezed out of the best jobs in Chicago because as a black man he was not allowed to join a union. But she said she had also been taught not to see race as a barrier, to look at the world in terms of what is possible, not the other way around.
“My parents told us time and time again, ‘Don’t tell us what you can’t do,’ ” she said. “ ‘And don’t worry about what can go wrong.’ ”
She talks on the campaign trail about high school advisers who tried to dissuade her from applying to Princeton because they thought her scores were not good enough. (She graduated with honors in sociology in 1985.)
She talks about college counselors who said similar things about her desire to go to Harvard Law, from which she graduated and went on to one of the top corporate firms in Chicago.
“I realized that gnawing sense of self doubt that lies within all of us is within our own heads,” she said in Atlanta. “The truth is we are more ready and more prepared than we even know. My own life is proof of that.”
Mrs. Obama’s father, Fraser Robinson, provided for the family of four on a city worker’s salary. Her mother, Marian Robinson, now 70, stayed home and allowed their two children only one hour of television a night.
Mrs. Obama and her brother were expected to fill their time with books, chess, sports — and, critically important they both said, dinnertime conversations with their parents.
The defending of ideas, the back-and-forth, the debates, they were an early in-home version of what Mrs. Obama has come to do, almost full-time now, for her husband.
At Harvard Law School, one professor recalled that Mrs. Obama was not one to mince words.
“Michelle was a student in my legal profession class in which I ask students how they would react to difficult ethical and professional challenges,” said the professor, David B. Wilkins. “Not surprisingly, many students shy away from putting themselves on the line in this way, preferring to hedge their bets or deploy technical arguments that seem to absolve them from the responsibilities of decision-making. Michelle had no need for such fig leaves. She always stated her position clearly and decisively.”
Mrs. Obama said her mother has been her No. 1 advocate and role model, even though their lives could not be more dissimilar.
“I remember Michelle telling me about a teacher complaining about her temper in elementary school,” said Verna L. Williams, a law professor in Cincinnati who has been a friend of Mrs. Obama since their days at Harvard. “She said her mom told the teacher: ‘Yeah, she’s got a temper. But we decided to keep her anyway!’ ”
Mrs. Obama is an organized and self-described “task master,” who has always been focused — so much so, that when she met Mr. Obama in 1989, when they were working at the same law firm in Chicago, she refused to go out on what Mr. Obama called “a proper date.”
“Eventually I wore her down,” he wrote in his memoir. During the summer when she met Mr. Obama, Mrs. Obama said she was influenced by his sense of purpose, and began to change her own career to add more service to others.
Martha L. Minow, a professor at Harvard Law School, did work with Mrs. Obama for a nonprofit educational group in Chicago. Dr. Minow’s father, Newton N. Minow, is senior counsel at Sidley Austin, the law firm where the Obamas met. Dr. Minow said she remembered hearing about the day Mr. Obama announced to her father that he would be leaving the firm to pursue public service.
“My dad was very supportive,” she said. “Then he said, ‘One more thing, I’m going to take Michelle with me.’ ”
And Mr. Obama did. Mrs. Obama left the firm, where she specialized in marketing and intellectual property, after two years and eventually founded the Chicago office of Public Allies, a national nonprofit leadership-training network for young adults.
After that, she gravitated toward the University of Chicago, whose campus is in her own South Side neighborhood. As a whole, the university has an often-tense relationship with the poorer surrounding area, and Mrs. Obama’s job, as vice president for community and external affairs at the university’s medical center, is to form partnerships between the two.
A recent project has focused on opening more neighborhood clinics to provide preventive care and take stress off the emergency room. Mrs. Obama earned a reputation as being equally tough on the hospital and the community in regard to their obligations to each other.
Now, she often describes her life to audiences in terms of beating the culture of low expectations that confronted “a little black girl” from the South Side.
“I wasn’t supposed to have my own successful career,” Mrs. Obama said in Atlanta. “They said my achievement must have been the result of racial preferences. And I am certainly not supposed to be standing here, maybe to become the next first lady of the United States.”
Asked about the role of first lady, Mrs. Obama said she saw it as a full-time job. But, she hastened to add, she reserved the right to change her mind if she gets there.