By Kathryn Westcott
As Americans choose their candidates for the 2008 presidential race, never before have so many spouses battled it out so publicly.
The 2008 campaign has seen the role of the political spouse reshaped, with potential first ladies - and one possible first gentleman - more than ever acting as independent surrogates for their partners.
Mrs Obama has been articulate and passionate
The past 12 months have seen Michelle Obama emerge as a formidable campaigner for her husband, drawing large crowds to her own scheduled events.
Outspoken, articulate, and independently minded, she has been widely seen as an asset to the Obama campaign.
The 44-year-old Ivy League lawyer has taken a much edgier role than the other candidates' wives: not shying away from going on the offensive where necessary.
She recently launched a scathing attack on Hillary Clinton, saying she represented "the same old thing over and over again."
She has not, however, gone as far as Bill Clinton, whose controversial role as Hillary's bad cop has drawn criticism from senior members of his own party.
Possibly because a woman for the first time stands a chance of winning the nomination for a major US party, spouses have seized the opportunity to express themselves and weigh in on issues.
There is no formal job description for a First Lady at the White House
Mrs Obama - who has taken time out from her high-powered job as a hospital administrator in Chicago - has been a crucial element in her husband's campaign to win over key voting groups, such as working women and African-Americans.
Her experience of growing up in a working-class black Chicago neighbourhood could been seen as more typical of the African-American experience than that of her husband, providing more connection with black working-class voters.
Her speeches have resonated with issues of race and the prejudice she encountered in her early years.
Unlike Barack, who has largely tried to avoid talking about race, Mrs Obama has raised the flag for the "little black girls" and highlighted "disparities that exist across the country."
Asset or liability
But she never forgets her own two young children, ensuring that voters know that she is home every night in time to put them to bed.
This is a very modern marriage, and the senator's wife has often spoken of juggling the demands of being a professional, a mother and wife of a politician who is away from home for long periods.
A community activist, she has described herself as committed to public service.
"Michelle Obama has been fantastic on the stump," says Robert P Watson, professor of American history at Lynn University in Florida, and the author of a number of books on the history of first ladies.
"She has great political instincts."
However, such spouse visibility can be either an asset or a liability.
In 2004, Teresa Heinz Kerry publicly waded into areas of policy and quickly became seen as a risk within Camp Kerry.
Mr Watson says that Mrs Obama has been careful to avoid discussing policy and strategy.
"She is a remarkably savvy operator," he says. "She brilliantly frames what she says within a safe, nurturing framework. Much of what she says comes through the eyes of a mother with two young children - in a way that doesn't really allow her to be a target."
Cindy McCain has played a more traditional, supporting role
Mrs Obama has said that politics is not her passion and that her role is to complement her husband's campaign.
Cindy McCain, wife of the Republican front-runner John McCain, has complemented her husband's campaign by playing a more traditional, supporting role.
She has, however, been more outspoken than she was in her husband's 2000 campaign.
A "military mom" with two sons in active service, she has criticised the Bush administration for what she says is its mishandling of the Iraq war.
But, she has resisted taking policy positions or criticising other candidates publicly.
The 53-year-old former Arizona rodeo beauty queen is seen as an asset to her husband's campaign, having long overcome the humiliating public exposure of her former addiction to prescription painkillers.
Potential turf war
The mother of four is a philanthropist and businesswomen in her own right. In 2000, she took over as chairman of her father's multi-million dollar Budweiser distribution company.
Eleanor Roosevelt broke new ground as an active First Lady
Mrs McCain has said that if she were to become first lady, she would continue her overseas volunteer work and encourage others to do so.
What do Americans expect from their first ladies?
There is no formal job description, although the first lady does get an office, a budget and staff.
"Over the years, first ladies have been White House managers, White House hostesses, White House renovators, co-campaigners, social activists and policy advocates," says Mr Watson.
Former President Mr Clinton would break new ground as "first gentleman", and questions have been raised about who would really run the affairs of the country if Hillary Clinton got into office.
'Finger on the pulse'
While Mrs Clinton has suggested that he might play the role of ambassador to the world, some commentators have suggested this could potentially spark a small turf war with a new secretary of state.
Given her biography, one would expect Mrs Obama to be a active first lady.
Bill and Hillary Clinton: Two for one again?
Mr Watson says that she does have the capacity to "re-write the books". But, he said that the issue of her being the first African-American first lady was a sensitive one and that she could "face a more difficult balancing act".
"I expect there would be public pressure for her to pull back," he says. For example, he thinks it would be unlikely that she would break new ground and continue to work.
"First ladies have to have their fingers on the pulse of public opinion," he says.
The public, however, are never entirely sure about what they want from a first lady.
"If she's independent, we're wary. If she's a prop, that's worse. A big career is an asset, unless she won't give it up," June Kronholz once wrote in The Wall Street Journal.
Eleanor Roosevelt used her influence as an active first lady to campaign for human rights, among other things. And Hillary Clinton moved the First Lady's office to the heart of power in the West Wing.
But Mr Watson says Mrs Roosevelt and Mrs Clinton both faced criticism after they left.
"The country suffered 'Eleanor fatigue' and 'Hillary fatigue'," he says. But, he said, first ladies are always criticised for either trying to do too much or doing too little. "It's a case of damned if you do, damned if you don't."
Laura Bush, who took over from Mrs Clinton, has been a more traditional first lady.
The expectation is that Mrs McCain will follow suit. She has said that she thinks the "American voter wants a traditional situation."
When asked recently what her "first lady platform" would be, Mrs Obama appeared wary of revealing too much. "To make sure my kids have their heads on straight," she said.