As the two most progressive candidates in the Democratic presidential primaries, Bernie Sanders and Elizabeth Warren should in theory be rivals trying to edge each other out. In the special lingo of punditry, Sanders and Warren are driving in the same progressive lane, while the other major candidates, Joe Biden and Pete Buttigieg, are travelling in the moderate lane. The logic of the “lane” metaphor holds that Warren and Sanders must aim to first go after each other and then try and defeat whoever is the most powerful candidate in the competing lane.

If the lane theory were true, Sanders and Warren would already have been sniping at each other and girding themselves for more of same on Thursday night’s debate in Los Angeles. But if the past is any guide, there won’t be any duel between Sanders and Warren on Thursday. While many journalists and also their own supporters might believe they are natural foes, Sanders and Warren have never acted as if that were the case.

Sanders and Warren are like two boxers who eschew combat even as they are surrounded by a mob yelling, “Fight, fight, fight!” They question is, why aren’t we seeing the battle so many people are egging on?

As Jonathan Martin of The New York Times notes, “Since the presidential primary race began, the two senators—who have been friends since before Ms. Warren was elected to the Senate in 2012—have abided by a de facto nonaggression pact, rarely criticizing one another and frequently acting as something of a populist tag team on the debate stage. And as Pete Buttigieg has risen in the polls and Joseph R. Biden Jr. has proved durable, Mr. Sanders and Ms. Warren have been happy to demonstrate their left-wing bona fides by contrasting themselves with the more moderate contenders.”

Martin himself belongs to the journalist camp that seems to be trying to gin up a battle. According to Martin, “It’s increasingly clear that their biggest obstacle to winning the Democratic nomination is each other.” As journalist Rachel Cohen tweeted, Martin’s article “is not subtle in its beg for a brawl.”

To bolster this argument, Martin quotes former representative Barney Frank, a prominent Warren supporter. “Sanders is a problem for her in two ways: one in terms of the votes that would otherwise go to her, and two, by forcing her to go to the left,” Frank claims. “Her ability to respond to concerns about electability is hampered by her concern that she’ll be overtaken by Sanders on the left.”

Some of Bernie Sanders’s more strident supporters share Frank’s belief that there’s no room for two progressive candidates. Leftist journals like Jacobin and Current Affairs have taken a strong line against Warren in recent months. As Politico notes, “In the pages of Jacobin, Warren has gone from seeming like a close second to Sanders to being a member of the neoliberal opposition, perhaps made even worse by her desire to claim the mantle of the party’s left. The magazine’s newest quarterly print cover makes this point explicit in illustration: Sanders and his new democratic socialist comrades in the House are pictured cycling on Team Red in a race against Joe Biden and Warren on Team Blue.” Writing in The Guardian, Current Affairs editor Nathan Robinson lambasted Warren, saying, “progressives no longer need to wonder whether she’s with us or not. She’s not.”

Yet, to date, the animus between Sanders followers and Warren devotees hasn’t manifested itself in the actions of the candidates or their campaigns. Sanders and Warren both seem to be operating on the theory that there is no zero-sum game on the left, where extra votes for one candidate can only come at the expense of the other. Rather, they are both betting the way forward is to expand the progressive base.

Crucially, the type of voters they are chasing are different. As CNN noted in July, “Their respective cores of support come from different places. Sanders, according to recent polling, enjoys a strong grip on younger, working-class and less-educated voters. Warren, meanwhile, has done better with older, college-educated voters, and polls stronger with women than Sanders.”

In other words, while Sanders and Warren might share adjacent ideological space, they aren’t at this stage competing for the same voters. Sanders is most likely to grow by picking up Joe Biden voters, while Warren’s main rival is Pete Buttigieg.

Given this reality, the Sanders/Warren truce is likely to hold for Thursday’s debate. The ultimate question of which one is going to be the progressive champion isn’t likely to become pressing until at least the first batch of primaries are over. After South Carolina votes, Sanders or Warren will be in a better position to make a case for themselves as leader of the progressive field.

But even after South Carolina, there might be compelling reasons for both campaigns to keep going, a real possibility given their fundraising strength. As The New York Times acknowledged, some progressives are hoping that if both candidates gather strength, they’ll be in position to have a combined majority of delegates, which would give them the ability to block any moderate candidate from winning the nomination.

Sanders and Warren both have eager fans who are ready to rumble. But the candidates themselves have been very cagey about keeping the fight focused on moderate Dems. Thursday’s debate will show if they are still holding to this strategy.