In theory, Bernie Sanders and Elizabeth Warren should be rivals fighting over the same real estate, leadership of the left wing of the Democratic Party. That’s certainly the way some of their followers see it. The socialist publication Jacobin has fallen into the habit of publishing articles trashing Warren, seemingly on the assumption that she’s the main barrier to Sanders’s consolidating control of the left and winning the Democratic presidential primary. Just hours before Thursday night’s debate, Jacobin ran a piece roasting Warren as a candidate who is “too late.” The thrust of its argument is that she is a reformist liberal who wants to salvage capitalism, a goal that might have worked decades ago but is no longer viable. Warren, the article contends, is “a very different candidate from Bernie Sanders. With a very different constituency. And, ultimately, [it’s] why it’s harder to imagine her delivering the type of change the United States desperately needs.”

The differences between Warren and Sanders are real. Warren calls herself “a capitalist to my bones,” while Sanders is a self-described democratic socialist. Yet on the debate stage, on crucial issues like health care and trade policy, Warren and Sanders clearly had more in common with each other than they did with the other candidates. In fact, they seemed to form a tag team in opposition to the front-runner, Joe Biden. At one point, Warren smiled when she saw Sanders making his characteristic hand gestures while disputing Biden.

Biden himself wanted to emphasize the commonality, noting that Warren “says she’s for Bernie, well, I’m for Barack.” Warren shot back by saying that she (and by implication Sanders) wanted to build on what Obama started: “We all owe a huge debt to President Obama, who fundamentally transformed health care in America and committed this country to health care for every human being…. And now the question is, how best can we improve on it?”

Sanders, as is his wont, was even more harsh in responding to Biden’s claim that Medicate for All would cost $30 trillion. “Well, Joe said that Medicare for All would cost over $30 trillion,” the Vermont senator shot back. “That’s right, Joe. Status quo over 10 years will be $50 trillion.” He went on to lash out at “the greed and corruption and price-fixing of the pharmaceutical industry.”

What’s striking is that Warren, a self-described capitalist, was equally savage in berating the for-profit health care industry. “I’ve actually never met anybody who likes their health insurance company,” she quipped.

Health care wasn’t the only issue on which Sanders and Warren formed a united front. As Peter Beinart of The Atlantic noted, “compare Warren + Sanders’ answers on trade to Harris, Buttigieg, Castro, Klobuchar. The divide on trade is even wider than on health care.” Sanders and Warren were critical of the outsize role of corporate power in trade agreements, and emphasized the need for labor unions and environmentalists to be represented in trade talks. As Warren said, “So our trade policy in America has been broken for decades, and it has been broken because it works for giant multinational corporations and not for much of anyone else. These are giant corporations that, shoot, if they can save a nickel by moving a job to a foreign country, they’ll do it in a heartbeat.”

Politically, it makes sense for Warren and Sanders to hold their fire against each other and to focus on Biden. Polling-wise, he remains the front-runner, while they are jostling for second and third place. Any path forward for them involves bringing him down.

But there’s another structural factor at work: Right now, Warren and Sanders are not competing for the same voters. As Jacobin notes, Warren supporters tend to be college educated, Sanders supporters not. Warren’s “coalition is richer and whiter than Sanders’s—in fact, Warren’s support is whiter than any of the other front-runners in the primary.” Sanders is more likely to gain voters from Joe Biden and Warren to gain voters from Kamala Harris or Pete Buttigieg. As long as they are not competing for the same voters, Sanders and Warren have the luxury of being magnanimous to each other.

Even with their different constituencies, both candidates have the same path going forward. Their first task is to either win or do well enough in Iowa and New Hampshire to install themselves as the front-runner: This will involve building up their base, rather than tearing down each other. After that, either Sanders or Warren would then have to expand that base in order to be not just the front-runner but also the dominant left candidate. That would entail either Sanders figuring out how to win over the suburban college-educated voters that, to date, are allergic to him or Warren finding out how to appeal to more blue-collar voters. But that competition isn’t likely to happen for another six months. Both candidates are thinking strategically.

But beyond strategy, there might be an ideological factor. Assuming that both Sanders and Warren would prefer a left-wing Democratic presidential candidate to a centrist, it could also be that they will support each other depending on who is leading in the spring of 2020. If that’s the case, there is little advantage in running each other down.

The 2020 campaign thus offers Democratic voters the choice of having not one, but two strong left-wing candidates, each with a different coalition. The unanswered question is which one will triumph in the primaries and thus be faced with the task of forging the two coalitions into one. But that’s a fight for another day, as both Sanders and Warren know.