After months of equivocation on the topic of health care, Elizabeth Warren firmly supported Bernie Sanders’s Medicare for All bill during the first Democratic primary debate of the 2020 presidential campaign. When the candidates were asked if they would support abolishing private insurance in favor of a single-payer program, Warren raised her hand before saying straightforwardly: “I’m with Bernie on Medicare for All.” Asked two days later if she stood by her answer, she didn’t budge: “Yes, I held my hand up. What part did you not see?”

It was a welcome development for single-payer advocates. As I wrote prior to the debate, Warren’s campaign has long been marred by her avoidance of discussing health care in a substantive way. While Warren was an original cosponsor of Sanders’s bill, she distanced herself from it in previous campaign appearances, often suggesting that there are “multiple pathways” to universal coverage.

Clearly, Warren’s campaign decided before the debate that it was time to take a stand on health care, which repeatedly polls as the most important issue to voters. By attaching herself more firmly to Sanders’s bill, Warren is committing to a single-payer program that guarantees comprehensive care to every American resident, free at the point of service. Her support has the potential to be a huge boost for the Medicare for All movement — but only if she embraces these specifics and defends them at every opportunity.

In other words, Warren will need to fundamentally change her campaign if she wants to truly demonstrate her support for single-payer. As of now, her website’s issues page still lacks a health-care section, and it remains to be seen how much she plans on centering Medicare for All in future campaign appearances. But Medicare for All faces incredibly powerful enemies, and it needs more than simple statements of support — it needs influential leaders like Warren fighting for it at every turn and staying true to its core principles.

Sanders, adding pressure to Warren and other candidates to embrace the specifics of his bill, issued a pointed statement following the debates:

Let us all be very clear about this: if you support Medicare for All, you have to be willing to end the greed of the health insurance and pharmaceutical industries. That means boldly transforming our dysfunctional system by ending the use of private health insurance, except to cover non-essential care like cosmetic surgeries. And it means guaranteeing health care to everyone through Medicare with no premiums, no deductibles and no copays. It is imperative that we remain steadfast in our commitment to guarantee health care as a human right and no longer allow private corporations to make billions in dollars of profits off Americans’ health care.

The statement was not so much a subtweet of Warren in particular as of the several candidates who support Medicare for All in name while hiding in ambiguity on the details. But Warren should take Sanders’s words to heart. If she really wants to advocate for single-payer health care, not just in words but in practice, she should make the policy a core issue in her campaign. This means following Sanders’s lead by bringing up Medicare for All unprompted in interviews and campaign appearances, remaining committed to the policy specifics, and relentlessly antagonizing the health-care profiteers who are trying to defeat it.

Warren possesses a powerful voice in the Democratic primary. With her reputation as a talented policy wonk, she can exercise some influence over liberals who criticize Medicare for All as unrealistic. Sanders has won millions of people over to the idea — he speaks directly to working people, and due to his advocacy as many as 70 percent of Americans now support his policy with strong support from Democrats, Independents, and Republicans alike. But many liberals remain opposed to the idea due to opposition from figures like Hillary Clinton, Joe Biden, and other establishment giants. As a candidate with a foot in both the progressive and establishment camps, Warren could be in a position to grow the Medicare for All constituency even further if she makes a genuine effort.

Sanders has long understood that the fight to win Medicare for All will require a massive struggle from both inside and outside the beltway. His theory of change revolves around the mass mobilization of working people, which is central to his campaign’s slogan: “Not Me, Us.” As he said in his closing debate statement, “nothing will change unless we have the guts to take on Wall Street, the insurance industry, [and] the pharmaceutical industry . . . if we don’t have the guts to take them on, we’ll continue to have plans, we’ll continue to have talk, the rich will get richer, and everybody else will be struggling.”

Warren’s newly emphasized commitment to Medicare for All is a very positive development, and single-payer advocates should be glad for her support. But we’re not going to win Medicare for All without a president who prioritizes it and mobilizes their supporters to fight for it.

It’s clear that Sanders has long been ready for this fight. Hopefully Elizabeth Warren is, too.