For the first time in over a decade, Barack Obama is a Medicare for All supporter.

On September 7 in Illinois, Obama promoted the idea while campaigning for Democrats ahead of the 2018 midterm elections. “Democrats aren’t just running on good old ideas like a higher minimum wage,” he said, “they’re running on good new ideas like Medicare for All.” His is the biggest endorsement from the political center for the idea, and a sign that Democrats are beginning to yield to this overwhelmingly popular demand — a recent Reuters/Ipsos poll showed that 70 percent of Americans support the plan.

But Medicare for All supporters should be skeptical of Obama’s support. Centrists are engaged in an ongoing effort to reinterpret what M4A means, which could lead to a watered-down proposal that throws the possibility of achieving single-payer health care into jeopardy.

Back in 2003, Obama spoke glowingly of single-payer , arguing that the only reason it might not happen “immediately” was that first, the Democrats would have to take back the White House and Congress. By 2009, Obama’s stated prerequisite for single-payer had come true. He himself occupied the White House, while Democrats held majorities in both the House and Senate. But by that point, of course, Obama had long abandoned single payer.

Centrist Democrats have a history of grinding down progressive policies into complex, unpopular, market-friendly schemes.

In fact, his administration worked to deliberately marginalize the idea and instead rallied support for the Affordable Care Act’s market-centered approach. They even dropped the planned inclusion of a public option when Senator Joe Lieberman threatened to filibuster the ACA in protest.

Ultimately, the powerful Democratic majority passed only a weak, fragmented plan with high costs and uneven benefits. While the ACA helped many people by expanding Medicaid and adding protections for people with preexisting conditions, it failed to combat the true source of the United States’ health-care crisis: the privatized multi-payer system that allows giant for-profit health companies to profit from Americans’ illnesses. Unsurprisingly, after voters replaced Obama with Trump, the key accomplishments of the ACA came under immediate threat.

In the wake of the ACA’s failure to lower costs and achieve universal coverage, single-payer has become a popular, viable demand. It was the lead plank of Bernie Sanders’s 2016 presidential platform and a regular applause line at his mass rallies . Sanders has kept Medicare for All in the spotlight, hosting viral town halls and releasing dozens of social media videos highlighting the plan’s benefits.

Sanders’s message is clearly resonating. Polling shows that Medicare for All now maintains majority support. Progressive candidates have successfully used the demand as a key campaign plank. And grassroots activists have found success taking the message to the streets, with groups like National Nurses United and Democratic Socialists of America running nationwide canvassing campaigns to build on the plan’s popularity.

Yet despite Medicare for All’s overwhelming popular support, many Democratic politicians have been reluctant to sign on. Sanders has earned sixteen cosponsors for his Senate bill , while its companion legislation in the House has 123. That amounts to only 34 percent and 64 percent of Democrats in the Senate and House, respectively — far lower than the 85 percent of Democratic voters who support the plan nationwide, according to the Reuters/Ipsos poll.

But that level of mass demand can’t be ignored forever. It has now become a litmus test for candidates.

Democratic socialists Alexandria Ocasio-Cortez and Rashida Tlaib campaigned heavily on Medicare for All while making waves this summer with upset primary wins in their bids for House seats. Andrew Gillum supported it on his way to winning the Democratic primary in Florida’s gubernatorial race. And nearly all prospective 2020 Democratic presidential candidates have expressed support for the plan, including Kirsten Gillibrand, Cory Booker, Kamala Harris, and Elizabeth Warren. Democrats are finally recognizing that they need Medicare for All — not rhetoric about “fixing the ACA” — in order to win.

Obama’s 180-degree turn on Medicare for All could cement the Democratic establishment’s shift into the M4A camp. It’s now likely that the congressional bills will have strong legislative support should Congress change hands. At the same time, centrist Democrats have a history of grinding down progressive policies into complex, unpopular, market-friendly schemes.

It’s going to take an unshakeable mass movement to win a system that actually provides health care as a right.

In order for Sanders’s vision of single-payer health care to succeed, the public must remain uncompromising in its demand for a truly ambitious Medicare for All — one that guarantees comprehensive care to every American resident as a single, public program and ensures a just transition that provides severance and jobs training to all workers whose jobs are impacted. Liberal think tanks and pundits are attempting to capitalize on Medicare for All’s popularity by watering it down, arguing that its meaning is ambiguous and could refer to something as meager as a Medicare buy-in — essentially a “public option” plan that would preserve the multi-payer system while allowing people to purchase Medicare coverage.

Given his record, it’s reasonable to expect that Obama will join this effort to co-opt Medicare for All and kowtow to the private insurance industry, the pharmaceutical lobby, and the American Medical Association, which have spent the last century using their power and influence to squash every effort to win a national insurance system. Democrats haven’t confronted this power in the past and, as shown in 2009, can’t be expected to do so even if they manage to take back Congress.

It’s going to take an unshakeable mass movement to win a system that actually provides health care as a right. That means no financial barriers to care — no copays , no deductibles, and no premiums. It means abolishing the private insurance industry once and for all. It means universal care with equal treatment for everyone — not means-tested coverage with a higher standard of care for the rich. It means a single, simple, and bold public program — not a public option that will leave millions underinsured and keep insurance profiteers intact.

Obama’s endorsement is a sign that the demand for Medicare for All is overwhelming. It will hopefully bring much-needed legislative support to the congressional single-payer bills. But Americans cannot allow the people who bungled the Affordable Care Act to undermine this fight, too. Medicare for All means nothing less than a universal, single-payer program that provides comprehensive care, free at the point of delivery. Obama’s support is welcome. But this time, we won’t accept any compromises.