Bernie Sanders and Elizabeth Warren both got good news on Friday from one of the major polls in the election cycle. The Des Moines Register/Mediacom/CNN survey enjoys the reputation for being the “gold standard” poll of the first primary state and has an outsize role in shaping expectations. Sanders came out on top in this poll, with 20 percent, followed by Warren at 17 percent, Pete Buttigieg at 16 percent, and Joe Biden at 15 percent.

The internal numbers in the poll paint a more positive picture for Warren and show the path she can follow to win. According to the Register, “Warren is viewed favorably by 70 percent of likely Democratic caucusgoers, the highest favorability rating among the 14 candidates tested. She also did well if you look at the combined first and second choice of voters. By that criteria, the pecking order looks like Buttigieg (60 percent), Warren (59 percent), Sanders (55 percent) and Biden (55 percent).

Breaking down the numbers further, Warren is the candidate who has the widest appeal across the factional divide that opened up in the party in 2016. As CNN notes, “She takes 19 percent of those who say they caucused for Clinton in 2016 and 20 percent among those who say they caucused for Sanders.” This level of support from both 2016 Clinton and Sanders supporters distinguishes Warren from her rivals.

CNN adds, “No other top tier candidate has as small of a gap as Warren. Buttigieg gets 18 percent among Clinton backers and 13 percent among Sanders’ 2016 supporters. For Biden, he gets 24 percent among Clinton caucus goers and 2 percent among those who caucused for Sanders. Like Biden, Sanders shows a very large gap. He’s pulling in 44 percent of his 2016 backers and a mere 4 percent of Clinton’s.”

Given these numbers, the natural pitch for Warren to make is that she’s the unity candidate, the one who can bring a fractured party together. And that’s exactly the message that Warren’s campaign has been banging on as they make the final push in Iowa. Last Tuesday, Julián Castro, who has emerged as Warren’s most high-profile surrogate, made the unity pitch at a Brooklyn rally. “The polling says, well, perhaps that a lot of older voters, go one way, right? And younger voters go another way,” Castro said. “You have a preponderance of younger voters that support Elizabeth and older voters that also support Elizabeth.… Elizabeth Warren is the candidate who can unite the entire Democratic Party.”

This unity message contrasts with Bernie Sanders’s electability argument, which is that he’s the candidate who can mobilize voters who either went for Trump in 2016 or sat out the election: working-class voters of all races as well as millennials.

As Washington Post reporter David Weigel tweeted, Warren and Sanders operate from “very different theories. From outset ($$$ to downballot campaigns) Warren’s was to make alliances so the party would accept her. Sanders’s is to win and make them put up with it, like the left always has to put up w moderate nominees.”

Warren and Sanders are having an argument that’s not really about policy but about strategy: what’s the best way to create a coalition that can defeat Trump in the Electoral College.

It’s this fundamental disagreement over strategy that sparked friction on Sunday after Politico reported that the Sanders campaign was giving volunteers a script that was critical of other candidates. The script was relatively tame: “I like Elizabeth Warren. [optional] In fact, she’s my second choice. But here’s my concern about her. The people who support her are highly educated, more affluent people who are going to show up and vote Democratic no matter what.” The script added, “She’s bringing no new bases into the Democratic Party.”

The release of this script caused a rare outburst of ill-will between the two campaigns, which have hitherto avoided criticizing each other except in the most elliptical fashion. “I was disappointed to hear that Bernie is sending his volunteers out to trash me,” Warren said. “I hope Bernie reconsiders and turns his campaign in a different direction.” Warren also used her remarks to hammer home her unity message.

“We all saw the impact of the factionalism in 2016, and we can’t have a repeat of that,” Warren cautioned. “Democrats need to unite our party and that means pulling in all parts of the Democratic coalition.”

Responding to the controversy, Sanders dismissed it as a media-manufactured argument. “I got to tell you, I think this is a little bit of a media blowup, that kind of wants conflict,” Sanders said. “No one is going to trash Elizabeth Warren.”

The quarrel with Sanders so perfectly allowed Warren to make her unity case that Jonathan Chait of New York magazine speculated that it might have been a calculated fight. “I wonder if Warren’s campaign is playing this up as part of her effort to detach herself from Sanders and play up image as ‘unity’ candidate who (unlike Bernie) can appeal across the party,” Chait tweeted.

Ryan Grim of The Intercept offered a similar analysis: “Looks like we have the outlines of Warren’s closing strategy: She’ll argue Biden can’t get it done and Bernie is too factional or divisive—note the quick reference to 2016—and that she’s the candidate who can unify the two wings.”

In the run-up to Tuesday’s debate, both Sanders and Warren are now competing with electability arguments based on radically different prescriptions—not just for how they can win the nomination, but also for how the Democrats can defeat Trump. Warren’s theory of the election is the more conservative one: It assumes Democrats already have a coalition large enough to defeat Trump and only need to bring everyone together. Sanders is offering a more transformational gambit: He’s betting that bringing new people into the electorate could shift both the nature of the Democratic Party and also crush Trump.

Perhaps the most useful thing about the primaries is that they’ll allow these theories to be tested. If Sanders can really bring out new voters, then he’s likely to swamp his competitors. Conversely, if Warren can in fact continue to draw from both those who supported Sanders in 2016 and those who supported Clinton, she’ll have her own path to victory.