On stage at debates, Sens. Bernie Sanders and Elizabeth Warren make a formidable team, deflecting attacks and amplifying criticisms of the more business-as-usual candidates. Off the stage, they avoid publicly disparaging each other, and their campaign staffers, with some notable exceptions, tend to do the same. Much has been made of this informal “non-aggression pact” between the pair, but as the Iowa caucus on February 3 approaches, some activists are beginning to ask how long this (relative) peace can last. Two progressive candidates may be better than one on debate night, but it might not be at the voting booth — where Sanders and Warren will inevitably split the electorate’s share of left-wing Democrats, preventing either from emerging as a dominant frontrunner. “We cannot sit on the sidelines as we watch this primary play out and allow a neoliberal be elected,” said Ana María Archila, co-president of Center for Popular Democracy Action, explaining CPDA’s endorsement of Sanders in December. “If we stay divided, the corporate Democrats will pick the nominee.” Nathan J. Robinson, editor of Current Affairs magazine and a Sanders supporter who has repeatedly made the case for harsher criticism of Warren, made a similar point: “Bernie represents a historic opportunity that must not be missed. If people sit on the fence for it, Biden may very well win this primary.” The same fear has inspired another group of progressive leaders to adopt a different tack, however. Democracy for America, the grassroots progressive group founded by Howard Dean in 2004 and which endorsed Sanders in 2016, told The Intercept they will decline to endorse before the first set of primaries. The goal, instead, is to make sure one of the two wins. “We see two extremely powerful and talented candidates that are both running excellent campaigns,” DFA Executive Director Charles Chamberlain said. Chamberlain pointed to the overlap in the two candidate’s goals on health care, a Green New Deal, and taxing the wealthy. Instead of picking sides, Chamberlain and DFA are planning to launch a coalition united by the shared goal of “defeating the corporate wing of the Democratic Party” and electing a progressive president — that is, either Sanders or Warren.

It’s not a dual endorsement — DFA says they may endorse one or the other candidate down the line — but rather, the coalition will serve as a space where left activists and organizations can work together to maximize the number of delegates captured by Sanders and Warren (collectively) and simultaneously continue building the goodwill and solidarity that will be necessary when progressive voters do eventually have to unite behind a single candidate. “The purpose of this coalition is to make unity possible down the line,” said David Segal, a progressive strategist and former Rhode Island state representative, “but it’s also to plant a flag in the ground and say to the media and the Democratic establishment: We plan to win. If Warren and Sanders together have a democratic mandate come convention, one of them is going to be president. That’s not negotiable.” Another priority for the initiative will be to ensure the delegates recruited to represent the candidates are unity-minded. If no candidate enters the nominating convention with a majority of delegates, there will be an opportunity for delegates to shift from one candidate to another. “We want Bernie delegates who are ready to support Warren as their second choice,” Chamberlain said. “And we have to have Warren supporters who are ready to go to Bernie at an open convention.” Once chosen, Chamberlain and Segal envision meet-ups for Sanders and Warren delegates to get to know each other and (hopefully) recognize their common goals.

Having both Sanders and Warren in the race winning delegates, some argue, may be the likeliest path to a progressive majority at the convention.

On the ground in Iowa, DFA and its partners plan to educate voters about strategic caucusing to maximize the two candidates’ delegate haul. Steve Cobble, a progressive activist who was delegate director for Jesse Jackson’s 1988 campaign, explained how this works. “If you’re a Warren supporter and she doesn’t meet the 15 percent threshold to be viable in your caucus site,” Cobble said, “you need to move over to Bernie on your second ballot.” In 2008, Cobble was responsible for convincing candidate Dennis Kucinich to tell his supporters to back Barack Obama on their second ballot — a decision that likely netted the future president a few extra delegates in his tight nominating contest with Hillary Clinton. For DFA, the unity approach arises out of strategic and organizational necessity. “Together, Warren and Sanders are supported by a supermajority of our members,” Chamberlain said. But those members are, for the moment, split about 50-50 between the two. The Working Families Party, which endorsed Warren in September, faced backlash from Sanders supporters among its membership. The ensuing dispute over its endorsement process — which involved balancing the input of grassroots members and a board of elected chapter leaders — ignited hostilities between Warren and Sanders supporters and damaged the WFP’s credibility with some activists. DFA may be hoping to avoid the same outcome. WFP communications director Joe Dinkin expressed sympathy for the unity message. “We’re with Warren, but both Warren and Sanders are giants of the progressive movement,” Dinkin said, “and they’re both building the strength of that movement and bringing new people into the fold. Half a dozen candidates are crowding the pro-corporate lane of the Democratic primary. It’s chaos. Progressives are lucky to have two strong, viable, and popular candidates in the race that are fighting to make America work for the many, not just the few.” When WFP endorsed Warren, they had hoped to inspire other groups to enter the fray. But the strong backlash may have discouraged more early endorsements. For the most part, unions have stayed out of the race as well. But waiting until an obvious frontrunner emerges to invest resources into the race risks allowing a moderate like Biden to consolidate his power uncontested.

“I do not abide by the idea that we should destroy our closest ally based on our differences, when we have so many goals in common,” Archila said.

That risk is what inspired Archila and CPDA to endorse Sanders. “We have a short window to make candidates of the left seem viable,” Archila said, “and to the extent that organizations representing workers and poor people and people of color sit it out, it’s going to hurt us.” Like WFP’s Dinkin, however, she praised both candidates and insisted CPDA’s endorsement is not intended to “disparage” Warren. As she sees it, the choice between staying neutral and going nuclear is a false choice — and a destructive one. “I do not abide by the idea that we should destroy our closest ally based on our differences, when we have so many goals in common,” she said. For the time being, Archila agrees with DFA that having both candidates in the race is good for the movement. “What we need is for both Sanders and Warren to stay on the debate stage for as long as possible so they can continue to define the contours of the conversation and together paint a picture of the country that is in deep contrast with Trump’s exclusionary, racist vision of America,” she said. Unlike journalists, activists, and Twitter warriors, she said, many voters are just tuning in to the primary. When they turn on their TVs, she wants them to see two candidates making the case for Medicare for All, ending deportation, and guaranteed housing. Otherwise, she fears the left’s ideas will be “marginalized” on a stage full of centrists. And indeed, the only place where real hostility between the Sanders and Warren camps appears to exist is online. “We did a lot of phone calls, meetings, and process to arrive at our endorsement,” Archila said, “and at no point did our people go ‘The other candidate is horrendous!’” Rather, she says, most were very enthusiastic about Warren. “What we heard was, ‘They both speak to us! How exciting!’” Other progressives see a similar trend. “There are way more people than it might seem who feel good about both candidates,” said DFA communications director Neil Sroka. “That’s the silent majority among progressives.” The unity coalition aims to maintain and cultivate that goodwill. Warren supporters are unlikely to enthusiastically join a Sanders campaign perceived as hostile to their candidate, and vice versa. Without cooperation, progressive leaders fear a circular firing squad and mutual destruction. In an email message to DFA members in December, Chamberlain warned that if supporters of Elizabeth Warren and Bernie Sanders “wage war on each other … [it] will take both of them down.” The point, Chamberlain told me, was this: “Let’s save our firepower for the corporate wing.” The effort also aims to address an obstacle that is a problem for Sanders in particular. The party power brokers have made no secret that they will do all they can to stop a Sanders nomination, which means that if he comes to the convention under a majority, and doesn’t have Warren delegates to lift him over the top, the party brass will unify around a different candidate. In the spring of 1988, when it briefly looked like Jackson may have been able to arrive at the convention as the delegate leader, party bosses began putting together their own “Stop Jesse” plan that involved nominating Mario Cuomo on the convention floor. In 1976, Jimmy Carter came into a divided convention with roughly 40 percent of the delegates, but was able to claim the nomination. Forty percent might have been enough for Carter, but it wouldn’t have been for Jackson, and it won’t be for Sanders. “In the Jackson ’88 campaign, we operated on the theory that a delegate who was not explicitly for Jesse would end up supporting his last remaining opponent,” said Cobble. “Bernie could possibly avoid that scenario with the help of other progressive Warren delegates.” Robinson, of Current Affairs, agreed that it’s important to avoid creating “so much animosity between the two camps that it becomes impossible to unify the left.” However, he sees a problem with being too coy about our differences. “Bernie might not want to criticize Warren directly, but he should certainly draw contrasts,” Robinson said, and he should be more willing to explain why he’s the better candidate. And as for Bernie supporters like him, “I think it’s important to actually criticize things about Warren’s record and politics and her whole method.” Bernie needs to take a more commanding lead over Biden and, Robinson said, “The obvious way to do that is to take those people whose first choice is Warren and second choice is Bernie and flip them.” David Segal maintains that Sanders is better off continuing to go after Biden voters. “Bernie’s recent tactic of drawing a more explicit contrast with Biden makes sense because Biden’s support is relatively soft — very few of his voters are enthusiastic about him — and in terms of raw numbers, it’s where the greatest number of second-choice Bernie supporters lie.” Meanwhile, Segal explained, hitting Biden serves the cause of unity. “The progressives who make up pluralities of the Sanders and Warren bases are generally unified in their critique of Biden. It’s a signal that they are all on the same team.” In other words, there are fewer votes to be had in attacking Warren, and it risks polarizing the more committed base of her supporters. “There is no coherent strategic rationale for the campaigns to attack each other,” Segal said. It’s often assumed in horserace coverage of the primary that Warren and Sanders are competing for the same voters; if one rises in the polls, the other drops. But that’s only partially true. Thirty-one percent of Sanders supporters pick Warren as their second choice, but 29 percent pick Joe Biden and another 9 percent pick Andrew Yang. Similarly, 32 percent of Warren voters pick Sanders as their second choice, but 22 percent pick Biden and 11 percent pick Pete Buttigieg. If Warren dropped out tomorrow, Bernie would gain some voters, but so would his moderate competitors. For instance, with Sanders polling at 20 percent and Warren at 14 in the Real Clear Politics average, Sanders would pick up about 5 percentage points if Warren dropped out, while Biden, who is at 30 percent, would pick up 3 and Buttigieg 2, the rest dispersed. Yes, Bernie gains, but Biden continues his climb toward 50 percent. Meanwhile, without Warren in the race, as Buttigieg fades, his supporters, who trend older and whiter, would be more likely to drift to Biden than Sanders, meaning that Biden would continue to pull away, unless Sanders could find a way to reverse that dynamic. According to Morning Consult, Biden is the second choice of the most Buttigieg supporters, at 27 percent, followed by Warren at 20 and Sanders at 12 percent. So if both Warren and Sanders stay in the race, the left rises if Buttigieg falls. If only Sanders is in the race when Buttigieg begs off, Sanders would fall significantly relative to Biden.

If Sanders, Biden, and Buttigieg all arrive at the convention splitting delegates three ways, it’s hard to see that contest tilting toward Sanders and not one of the moderates.