TALK about a head-spinner. Just a few days ago, Joe Biden's candidacy (for the Democratic Party nomination for the US presidency) was being prepped for burial, while Bernie Sanders' revolution was considered unstoppable. But after the Biden blowout in South Carolina, Super Tuesday voters decided to shake things up.

As the results came rolling in, from east to west, political anchors delivered a breathless play-by-play of how Mr Biden and Mr Sanders were divvying up the map and turning this into a two-man race. Their remaining major rivals, Elizabeth Warren and Michael Bloomberg, registered as little more than afterthoughts. Ms Warren came in third in her home state of Massachusetts, behind both Mr Biden and Mr Sanders.

And so, after all the tumult, the Democratic race has come down to this: Two straight white septuagenarian men fighting over the soul of the party - whatever that turns out to be.

Mr Biden and Mr Sanders have many fine qualities. Either would make a better president than the unstable man-child currently degrading the office. That said, for the party of progress, youth and diversity, a final face-off between two lifelong politicians born during World War II leaves much to be desired. And it says something depressing about the challenges female candidates still confront in their quest to shatter the presidential glass ceiling.

Different political styles

In the early days of this race, voters had a range of women to consider, some more conventionally qualified than others. There were four senators, a congresswoman and a self-help guru who varied in age, race, personal background and professional experience. They hailed from different regions, had different political styles and visions and espoused different policies.

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One by one, these candidates fizzled and fell away: Senator Kirsten Gillibrand of New York, who had pitched herself as a champion of women's issues; Senator Kamala Harris of California, the tough-talking former prosecutor; Marianne Williamson, with her premonitions of dark psychic forces; and Senator Amy Klobuchar of Minnesota, the Midwestern moderate who hit her high point with a third-place finish in New Hampshire. Representative Tulsi Gabbard of Hawaii is hanging on but has never been more than a curiosity.

For a while last autumn, Ms Warren was the candidate with the mojo. But she came under heavy fire from her rivals, seemed to flip-flop on Medicare for all, stumbled and never recovered. Faring poorly in the early contests, she all but vanished from the discussion. Even before Tuesday, her campaign acknowledged that a path to the nomination would require her to somehow triumph at a brokered convention. Put more simply: She's done.

It's impossible to know the degree to which gender factors into a candidate's political appeal, or lack thereof, especially at the presidential level. Man or woman, winning the presidency is not merely - or even largely - a question of merit. Americans are forever seeking that indefinable spark - a secret blend of strength and likability, authority and relatability, a talent for inspiring and connecting with voters.

Ms Warren is thought to have struggled in part because she was too professorial to connect with anyone beyond white college-educated women like herself. But had she focused on her up-by-the-bootstraps biography, who's to say she wouldn't have been slammed as inauthentic or as trying too hard? As for complaints that she was too strident or shrill or hectoring or inflexible, have any of these critics seen Bernie Sanders? Come on.

This is one of the vexing realities that plague highly accomplished female candidates like Ms Warren or Hillary Clinton, women whose résumés outstrip those of many of their male rivals. They have been told their whole lives that they have to outwork and outperform the men in order to be taken seriously - only to discover that it's not enough. It was one thing when Mrs Clinton lost the 2008 primary to Barack Obama. Despite his relative inexperience, he was a rare political talent with the added appeal of making history as America's first black president. But to lose in 2016 to Donald Trump? Winning the popular vote is cold comfort in a race that should never have been close.

Or consider Ms Klobuchar's conspicuous irritation with Pete Buttigieg's precocity. On multiple occasions she noted that a woman with his résumé - a 38-year-old former mayor of the fourth-largest city in Indiana - would never be taken seriously. "Women are held to a higher standard," she said at the November debate. "Otherwise we could play a game called 'Name Your Favourite Woman President,' which we can't do because it has all been men, including all vice presidents being men." Whatever your feelings about Mayor Pete, Ms Klobuchar was not wrong.

It's hard for any candidate to get the formula right. For women, it is harder because of a host of unconscious biases.

Overriding concern

As often noted, there have been reams of research on this topic, most of it discouraging. The problem goes beyond voters who hold traditional views of gender roles or admit that they wouldn't be comfortable with a Madam President. More subtly, ambitious women are viewed more negatively than men, while women leaders are often considered less legitimate than men, in the United States, at least.

Studies also show that women candidates are regarded as inherently less electable. You see this in polls where a high percentage of respondents claim that they are ready to elect a female president, but far fewer believe that their neighbours are. That perception has had particular resonance in a cycle where a candidate's ability to beat Mr Trump has been the overriding concern for most Democrats. And with the sting of Mrs Clinton's defeat still painful, many in the party were hesitant to take a chance on another woman.

Last summer, a poll on perceived electability by Avalanche Strategies found that gender appeared to be a bigger issue than "age, race, ideology, or sexual orientation". When voters were asked whom they'd pick if the primaries were held today, Mr Biden came out ahead. When asked whom they would make president with the wave of a magic wand, without the candidate needing to win an election, voters went with Ms Warren. Women were more likely than men to cite gender as a concern.

Nate Silver of FiveThirtyEight lamented that such anxiety can become a self-fulfilling prophecy. "So there are a lot of women who might not vote for a woman because they're worried that other voters won't vote for her. But if everyone just voted for who they actually wanted to be president, the woman would win!"

Early on, there was speculation that this time the dynamic would be different. With multiple women in the running, perhaps the discussion could move past the tired trope that says: Of course, I'd support a woman for president, just not that woman. It's something to think about over the next few months as we're watching two old guys fight for the privilege of taking on another old guy in November. NYTIMES