The truth about this week’s clash between Senators Bernie Sanders and Elizabeth Warren is that it’s not really about Bernie Sanders and Elizabeth Warren.

It is partly about them, of course: about whether Mr. Sanders told Ms. Warren 13 months ago that he did not believe a woman could be elected president, as she says he did and he says he didn’t. But the bigger picture is The Electability Question, a conversation so well worn it may as well be a proper noun.

Because only one woman is polling in the top tier of the Democratic primary race — and much of the conversation surrounding her is not about whether she should be elected, but whether she can be.

In Tuesday’s debate, Ms. Warren addressed that dynamic directly.

After the allegation was reported on Monday, it was inevitable that it would come up on the debate stage. Both campaigns had signaled before the debate that they had little interest in litigating it further. But instead of dismissing the line of questioning altogether, Ms. Warren pivoted to the broader issue of “electability.”

“Bernie is my friend, and I am not here to try to fight with Bernie,” she said after a moderator asked her about the remark she says Mr. Sanders made during a private meeting in December 2018. “But look, this question about whether or not a woman can be president has been raised, and it’s time for us to attack it head-on.”

Ms. Warren then pointed out that she and Senator Amy Klobuchar of Minnesota were the only people onstage who had never lost an election. This is an argument the women in this race have made repeatedly: Of course they can win elections; they already have.

“Look at the men on this stage: Collectively, they have lost 10 elections,” Ms. Warren said. “The only people on this stage who have won every single election that they’ve been in are the women, Amy and me.”

She argued that she would be more electable against Mr. Trump than a candidate “who can’t pull our party together, or someone who takes for granted big parts of the Democratic constituency” — an implicit reference to more moderate candidates in the race.

Mr. Sanders, for his part, again denied making the remark and said he would campaign wholeheartedly for either of the women onstage if they won the nomination.

“Hillary Clinton won the popular vote by three million votes,” he said. “How could anybody in a million years not believe that a woman could become president of the United States?”

But many don’t.

An Ipsos poll in June 2019 found that 74 percent of Democrats and independents would be comfortable with a woman president — but only 33 percent believed their neighbors would be. And many Democratic voters, including women, have spent the past year expressing their doubts quietly in interviews. They would be thrilled to elect a woman, they say, but what about those swing voters in Wisconsin?

Statistically, the idea that women are less electable is a myth. Studies have shown that when women run, they win at the same rates as men. In 2018, in fact, nonincumbent women did better than nonincumbent men in primary and general elections, according to the Center for American Women and Politics at Rutgers University. In Michigan, one of the three states that swung the 2016 election to President Trump, Democratic women were elected governor, secretary of state and attorney general.

But the continual debate over whether any given woman is electable places the burden on that woman to convince voters of what research has already shown. This is a burden men running for office don’t have.

“Women often have to run dual campaigns: a campaign of belief to convince donors and elites they can win, in addition to the main campaign,” said Amanda Hunter, research and communications director at the Barbara Lee Family Foundation, which supports women in politics. “That is the challenge Senator Warren is facing now, the constant drumbeat of doubts and questions regarding her electability.”

In other words, the fact that popular beliefs about who can win are inaccurate is not quite the point, because those beliefs can become a self-fulfilling prophecy. And that is what Ms. Warren is trying to prevent.

When voters who like a female candidate choose not to vote for her because they don’t think enough other people will vote for her, she can become less electable simply by virtue of being perceived that way. And inasmuch as the dispute between Ms. Warren and Mr. Sanders affects public opinion of women’s electability, the very existence of the dispute poses a threat.