In a recent interview with New York Magazine Alexandria Ocasio-Cortez commented that “in any other country, Joe Biden and I would not be in the same party, but in America we are.”

With consistent cries for party unity since before presidential candidates even began announcing their campaigns, it would be tempting to attack Ocasio-Cortez as splitting the party, but she is absolutely right. There is only a unified party to split on paper. America’s winner-take-all style of voting forces disparate political interests to share a title and to pool donors—unless they have the ability, like AOC, to source their own funding.

The GOP has used this to their advantage, emphasizing social wedge issues like abortion and immigration to pull working-class white voters away from their economic interests on the left—convincing them to cheer on tax cuts for the ultra-wealthy. For the Democrats, however, the powerful faction of the party that represents professional-class interests—the private-public partnership, means-testing, social-program-cutting wing—has represented a barrier to participation for truly progressive candidates and voters.

That’s why it has been heartening, prior to this week, to see Bernie Sanders and Elizabeth Warren avoiding the temptation to attack one another. While many of Bernie’s supporters online have adopted toxic attitudes toward anyone other than their preferred candidate, and many Warren supporters have questioned Bernie’s feminist bona fides (particularly in light of that toxicity from many “Bernie Bros”), the candidates and their campaigns seemed largely cordial and supportive of one another. It’s important, as the marginalized left-wing of the party, to focus on commonalities and mutual aid if there is going to be any hope of overcoming the powerful centrist forces that have ruled the party and served moneyed interests with only moderately less zeal than the Republican party.

That shared effort began to fall apart on Saturday night whenPolitico ran a story under the headline “Bernie Campaign Slams Warren as Candidate of the Elite.” The story included excerpts from a document purported to be circulated within the Sanders campaign, with scripts instructing volunteers how to attack rivals in the Democratic primaries. While criticisms of Joe Biden and Pete Buttigieg are hardly surprising, the attacks on Warren—noting that her supporters are predominantly educated, affluent voters who “who are going to show up and vote Democratic no matter what”—came as a surprise in the context of the candidates’ established alliance.

Skepticism in these cases is usually warranted, but the article contained little to suggest that the content was anything less than official and approved by Bernie Sanders himself. By the time Sanders came forward to repudiate the document and deny its official status, the damage was done. The rift was already beginning to widen.

Warren responded that she was “disappointed to hear that Bernie is sending his volunteers out to trash me,” and she sent out a fundraising email that asked both for donations and for supporters to share personal stories and perspectives to contradict the framing of her base as elitist. If that had been all, then it might have been easy to move on and return to a mutually supportive stance within a few days. But the real damage was done when people close to Warren, perhaps in an effort to retaliate, spoke to CNN about a private conversation the two had in 2018.

Back then, the thought of actual voters making actual choices seemed distant and abstract, and the candidates sat down to discuss strategies against Trump and to establish the general truce that has held until now. Everyone involved seems to agree on those points, but differing reports emerge when it comes to the topic of gender.As CNN reported, Warren laid out her strengths as a candidate: “She could make a robust argument about the economy and earn broad support from female voters.” Bernie was not on the same page.

According to anonymous members of Warren’s team, Bernie didn’t think a woman could win. Bernie shot back with his own version of events, saying, “It is ludicrous to believe that at the same meeting where Elizabeth Warren told me she was going to run for president, I would tell her that a woman couldn’t win… What I did say that night was that Donald Trump is a sexist, a racist and a liar who would weaponize whatever he could. Do I believe a woman can win in 2020? Of course! After all, Hillary Clinton beat Donald Trump by 3 million votes in 2016.” When Warren herself was finally convinced to weigh in directly, she urged people to move on, claiming that she was more interested in what she and Sanders agree on… But she also confirmed the more inflammatory version of events: “Among the topics that came up was what would happen if Democrats nominated a female candidate. I thought a woman could win; he disagreed.”

While there is certainly a conversation to be had about to what extent America remains too sexist to support a female candidate, it seems like a stretch to accept the idea that, in 2018, Bernie would hold such a categorical view against the possibility of a woman being elected president. What makes it particularly questionable is the existence of footage from a C-SPAN appearance three decades earlier, in which Bernie says, “In my view, a woman could be elected president of the United States. The real issue is whose side are you on? Are you on the side of workers and poor people, or are you on the side of big money and the corporations?”

The suggestion that Bernie’s views have become more regressive since 1988 seems far-fetched. The inclusive, forward-thinking persona he has consistently presented to the public for 40+ years doesn’t line up with this supposed private view. Then again, the idea that Warren would simply lie about Sanders’ comments seems equally unlikely. Who you believe seems to depend largely on who you prefer, and the two camps seem to be moving further from each other as the Iowa Caucuses close in. On one side, Bernie Sanders is a sexist; on the other, Elizabeth Warren is a liar.

Without a recording or a transcript of the conversation, it doesn’t seem quite justified to land in either of those camps. Without third-party witnesses, the basic facts of who did and who said what can quickly dissolve. The message that was intended and the message that was received crystallize in each person’s mind to the point that they become irreconcilable. Perhaps Bernie did think that a progressive man was better poised than a progressive woman to counter Donald Trump’s brand of populism in the 2020 election. Maybe his way of saying so was so clumsy that Warren took it as a broad statement about the viability (or lack of viability) of female candidates, and she recounted it as such to people close to her. Short of calling either of them a liar or worse, that is the best I can muster—a version of events that I prefer to believe in order to maintain my respect for both of these candidates.

Supporters from both sides will no doubt find this middle-ground unsatisfactory. The rift feels real right now, and it’s starting to seem like each side is trying to undermine the chances of the other. But while only one candidate can win the nomination, in the end, their support draws too much from the same pool of voters to allow this rift to remain. Already Bernie supporters who also donated to Warren are turning against her with the hashtag #RefundWarren. But the sad truth is that neither can win in the general election without support from the other’s ardent fans. And who really stands to benefit from continued fighting? The center and the far right. It can only help Joe Biden and Donald Trump. And Donald Trump seems to know it…

If Sanders and Warren can’t each count on the other’s supporters to get behind them as the primaries shake out, then Biden will likely hold onto his narrow lead. And if one of them does manage to get the nomination with this acrimony still hanging in the air between them, no amount of campaigning for one another is going to muster the sort of passion that we can count on to overwhelm Donald Trump in the general. 2016 should have taught us that much.

This feud needs to end now. Warren and Sanders need each other, and our country needs them. They are the only candidates taking America’s economic divide seriously, and the only candidates willing to tackle climate change with the resolve and transformative action it requires. If Donald Trump gets reelected, he will continue to make both of these problems far worse, destroying hope for economic justice and a sustainable future. If Joe Biden is our next president, then we will go back to enacting middling, inadequate reforms—one step forward for every two steps back.

Warren and Sanders, united, represent our only real hope. Of course, they each believe that they are best suited to the job. They wouldn’t be running otherwise. But if either of them is going to win, they need to come together, reaffirm progressive unity with one voice—acknowledging the differing accounts of events and decrying sexist limitations. Either of them can win this election, but neither can do it alone.