If Vice President Joe Biden opts to run for the Democratic presidential nomination, he will face an unusual potential barrier for a male politician: his gender.
Democratic activists say they like Hillary Clinton largely because of her experience and progressive policy views. But another major factor in Democrats rallying around Clinton's candidacy has been the chance to elect the first woman president.
The liberal group Emily's List launched a campaign back in 2013 called "Madam President," with events around the country touting the idea of a female Democratic candidate in 2016. A bloc of the Democratic women serving in the Senate, including Massachusetts' Elizabeth Warren, that year sent Clinton a letter, urging her to run.
Since Clinton launched her campaign, a number of celebrities have spoken of her candidacy in historic terms, such as when actress Jennifer Lopez said, "it's time for a woman president." The majority of Clinton's campaign donors have been women, and many of them have highlighted the importance of electing a woman as president.
Some liberal men too have emphasized Clinton's gender as part of the significance of her candidacy. Bill Burton, a former senior Obama aide, wrote earlier this year, "the fact that she's a woman is not determinative of my support, but it is important."
Democrats acknowledge some new wariness about Clinton's chances of winning a general election, seeing the drop in her poll numbers over the last few months amid the controversy over her use of e-mail as secretary of state. But Biden, if he opts to run, will face a party reluctant to push aside a strong chance to nominate and then elect the first woman as president.
My politics "are closer to Bernie Sanders," said Gina Glantz, who was a senior adviser to the presidential campaigns of Bill Bradley (2000) and Howard Dean (2004). "But I'm 72 years old, and I want there to be a woman president before I die and she is my shot."
Glantz, who now helps run a group called Gender Avenger that pushes for the inclusion of women on panels and in other public forums, said, "a lot of women, with Hillary Clinton running as long she's been running in this race, have said 'I'm ready for a woman candidate,' and he [Biden] is not going to be able to pull those women away."
To be sure, Clinton's gender presents its own challenges. The candidate has acknowledged the idea of a "hair and make-up tax," namely that women have to spend more time getting dressed for work because their physical appearances are more scrutinized than men.
While polls suggest most Americans are comfortable with a female president, that remains untested at this point, since all 44 presidents have been men and no woman has ever been a major party presidential nominee. And women still struggle to get elected to other offices, as only there are only 20 female members of the U.S. Senate.
And identity often does not align with politics. Female candidates sometimes lose the women's vote, male voters often don't back male candidates.
In the 2008 Democratic primaries, nearly 60 percent of women in states like Maryland and Virginia picked Obama over Clinton.
Back then, a number of high-profile women, such as then-Kansas Gov. Kathleen Sebelius, Caroline Kennedy, and Missouri U.S. Sen. Claire McCaskill, endorsed Obama over Clinton.
"None of these women will back Clinton just because they feel like they have to because she is a woman," said Kelly Dittmar, a scholar at the Center for Women and Politics at Rutgers University. "Many didn't do so in 2008, and they won't in 2016 if they identify another candidate who they view as better or more viable."
Women are generally more liberal than men, and both Biden and Vermont Sen. Bernie Sanders, Clinton's current leading opponent in the primary, are firmly on the left politically.
Sanders is already doing well among Democrats overall, including women, particularly in New Hampshire, where he leads in some polls over Clinton. Biden was on the ticket in 2012 with President Obama as the two carried 55 percent of the women's vote.
But so far, the "Draft Biden" movement's most high-profile figures are men: Josh Alcorn, who was a fundraiser to Biden's late son Beau, and ex-South Carolina Democratic Party chairman Dick Harpootlian.
Of the Democratic senators who are women, 10 have already endorsed Clinton, even as they knew Biden had not yet closed the door to a run. A majority of the women who are members of House of the Representatives have also backed the former first lady.
This in part reflects the overwhelming support of Clinton from the Democratic Party's establishment. Of the 31 male Senate Democrats, 16 of them have also already backed Clinton. But many of the female lawmakers have framed their backing of Clinton in terms of the historic nature of her candidacy.
"I am proud to support Hillary in her effort to shatter that highest and hardest glass ceiling that has been cracked but not yet BROKEN," Sen. Patty Murray of Washington wrote in a Facebook post in April.
Clinton and her supporters are careful not to suggest women will line up behind the former first lady simply because of gender.
And Clinton herself has not made her gender an explicit focus of her campaign.
But unlike in 2008, the former first lady is not downplaying the significance of her candidacy in terms of gender. She joked in her June kickoff speech that she would be "the youngest woman president in the history of the United States."
"There will certainly be women who will be both excited to vote for Clinton, and to vote for a woman. The other driver is the demographics of a Democratic primary. It's overwhelmingly female. Whatever candidate can speak to women's concerns—not just things like abortion, but child care, tolerance, income inequality, education—will have a natural advantage with a majority of the primary electorate," said Margie Omero, a Democratic pollster who has written extensively about the important of the women's vote for Democrats.
Amid the e-mail controversy, many Democrats have started to voice concerns, particularly privately, about Clinton's strength as a general election candidate. And Warren, despite signing the 2013 letter, has praised Sanders during the presidential campaign process, not Clinton.
But some of Clinton's most prominent defenders the last few months have been her former Senate colleagues, California's Dianne Feinstein and McCaskill of Missouri. And while that support is not framed in terms of gender, that kind of elite backing from prominent women could help Clinton weather a challenge from Biden.
"Among political women in the Democratic Party, I think there is a sense of shared experience and pride in the possibility of a woman holding the nation's highest office," said Dittmar. "Among some there may be that sense that she's been in the trenches with them, especially when confronting gender-based hurdles that still for exist for women in politics."