Hillary Clinton is trying to go where no woman has gone before - to the White House.
Other women have run for the country's highest office - from Shirley Chisholm to Elizabeth Dole. But never has a woman had such a good chance first to capture her party's nomination, then to win the presidency.
So this time it could happen - the United States could have a woman president. Is the country ready for that?
Perhaps the most amazing thing is that in the 21st century, that question is even being asked.
Clinton is certainly benefitting from tremendous strides women have made in all aspects of politics over the past generation. But the fact that this barrier still exists in the United States shows that the old attitudes have not totally disappeared.
A short list of the countries that have already crossed this gender threshold, some long ago, includes Britain, India, Israel, the Philippines, Iceland, Ireland, Chile, Germany, Nicaragua, Sri Lanka and Liberia. All told, there have been some 36 women chief executives in the world. A woman is in today's runoff for the presidency of France.
But the United States, the country that has long seen itself as the cutting edge of democracy, has yet to even nominate a major party candidate from among the group that represents the majority of its population.
"It's not just a president; we haven't had a woman vice president, or women as majority in either of the houses of Congress," says Robin Gerber, author of Leadership the Eleanor Roosevelt Way. "Nor have we made really great progress on any level since the so-called era of women."
How could that be?
The answer is probably a rather complicated mix of the historical, the anthropological and the political.
Historically, women were always at the bottom of the political totem pole in the United States.
"One of the things that strikes me is that in the United States, manhood was more exclusively associated with electoral politics than elswhere," says Robyn Muncy, an associate professor of history at the University of Maryland, College Park.
She points out that first voting rights were given to white males, then, after the Civil War, to black males. Women were the only ones excluded. That contrasts with European cultures where class and property determined voting rights. A woman of a higher class might not have had the right to vote, but she was definitely higher on the political heirarchy than a lower-class man, who also was denied the electoral franchise.
Shawn Parry-Giles, who is an assistant professor in the Department of Communications at the University of Maryland, notes that, despite its self-image, the United States has never been on the cutting edge of this issue.
"Historically, the United States was slow to give women the right to vote. Other countries did it sooner," she says. "This country has always been a little lagging, so it is not surprising it still is.
"We consider ourselve the beacon of freedom, but our hypocrisies always get in the way of that."
Muncy notes that the argument women made first to get the vote and then to get into office now works against them.
"Women argued very effectively that they were different, more nurturing, peaceful, cooperative," she says. "It was a good argument, but it had the effect of associating women with only a portion of the political issues."
And those it did not associate women with - things like the budget, foreign policy, military leadership - are exactly the ones associated with executive positions. This might be why women have done better running for legislatures than when they seek to be the executive, whether mayor, governor or president.
There are other historical factors that take on anthropological trappings. Consider the fact that Americans have always talked about the Founding Fathers, that George Washington was always the Father of his Country.
Add to that the institutionalization of the first lady in the country's political hierarchy - something rarely the case with spouses of leaders in other countries - and you have an office that has been effectively gendered.
"If you look at a survey of what people say are the traits of a leader and you overlay them with what people think are the traits of men and women, the overlay greatly favors men," says Gerber, a senior fellow at the University of Maryland's Smith School of Business. "So, for instance, to be a good leader, you are supposed to be a decision-maker. And men are considered to be good decision-makers."
Laura Liswood, secretary general of the Council of Women World Leaders, a group of female former heads of state, says this gap is particularly acute in the United States because the president is the commander in chief of the military, a domain always considered masculine.
"But those perceptions remain as obstacles for women trying to become president," Liswood says. "We are getting rid of some of those speed bumps."
Still, these perceptions put women candidates in what has been called a double bind. In order to appear to be a credible leader, they must adopt characteristics usually associated with masculinity. But in doing that, they risk criticism that they are not acting like women.
"They have to decide: Should I be considered nice or should I be respected?" Liswood says. "Men get to be both."
So, it is no surprise that some of the iconic pioneer female leaders - Margaret Thatcher and Golda Meir come to mind - are remembered for their toughness, their ability to match men in characterisitics usually associated with masculinity. Nor is it a surprise that female leaders considered more gentle, like Mary Robinson of Ireland, win more ceremonial posts, like the Irish presidency.
Liswood thinks that might be changing, with some voters looking for women to bring a different style of leadership, while not doubting their abilities to be decisive when needed. She points to Michelle Bachelet in Chile and Ellen Johnson-Sirleaf in Liberia as examples.
"That probably works better in a country that does not put so much emphasis on the commander-in-chief notion, the whole world superpower kind of thing," Liswood says. "It is a double bind that gives women a narrow band and Hillary has to walk it."
Part of the problem, Karen Kauffman, associate professor of government and politics at the University of Maryland, points out, is that politics is conducted in the United States in a traditionally masculine way.
"We like to play politics as a blood sport," she says. "All the frames around the election, the way we discuss politics, the way it plays out - it's not about building bridges or consensus, it about stabbing your opponent to death.
"I don't want to traffic in gender stereotypes, but on the average, women are more conflict-averse, less likely to enjoy overt displays of violence and conflict and less likely to engage in violent activity," says Kauffman.
Again, the double bind emerges - if a woman runs a campaign to win she runs the risk of being labled unfeminine.
One problem with gauging exactly where the United States is on the question of a woman president is that there is only one viable female candidate, Hillary Clinton. So much of the way people respond to the question of a female president is tied up in the way they respond to her.
Liswood say that if two or three other women were in the race, "it would be a different dynamic.
Kauffman agrees. "In my mind, when people are asked if they would vote for a woman president, they are being asked about Hillary Clinton, which comes with its own positives and negatives."
The biggest obstacle facing women, many agree, may simply be the inertia built into the American political system. In countries with parliamentary systems and numerous political parties, many different kinds of candidates can emerge, different genders, different ethnicities, different political beliefs.
But in the United States, only two get to run. That makes it difficult for any unrepresented group - women, blacks, Hispanics or Green Party believers - to get to the top of the politcal food chain.
"It is very hard to get the nomination," says Thomas F. Schaller, a political science professor at the University of Maryland, Baltimore County. "So the notion of whether the country would vote for a woman president has not been tested because neither of the two parties has ever nominated one."
Schaller thinks demographics will have a lot to do with changing that as women are now the majority of registered voters by about 53 percent to 47 percent. He sees Clinton focusing her campaign on younger unmarried working-class women, a growing group that was raised in an era of women taking top positions in the private and public sectors.
"It would only take a few of these women to get off the sidelines" for a Democratic victory, Schaller says.
And if that victory goes to a woman, the shape of American politics could be altered forever.
Gerber notes the huge effect having Nancy Pelosi as speaker of the House has had on the perception of women as leaders. "Magnify that by a thousand times if there's a woman president," she says.
Liswood tells the story of Vigdis Finnbogadottir, president of Iceland from 1980 to 1996, going around her country halfway through her 16 years in office.
"She was talking to children who were under 8 years old," she says. "Boys asked her if it was allowed for a man to be president."
WOMEN IN ELECTIVE OFFICE, 2007
Women hold 86, or 16.3 percent, of the 535 seats in the 110th US Congress -- 16, or 16.0 percent, of the 100 seats in the Senate and 70, or 16.1 percent, of the 435 seats in the House of Representatives. In addition, three women serve as delegates to the House from Guam, the Virgin Islands and Washington, D.C.
Statewide Elective Executive:
77 women hold statewide elective executive offices across the country; women hold 24.4 percent of the 315 available positions. Among these women, 48 are Democrats, 26 are Republicans, one is an independent and three were elected in nonpartisan races.
In 2007, 1,734, or 23.5 percent, of the 7,382 state legislators in the United States are women. Women hold 423, or 21.5 percent, of the 1,971 state Senate seats and 1,311, or 24.2 percent, of the 5,411 state House seats. Since 1971, the number of women serving in state legislatures has more than quintupled.
[Center for American Women and Politics]