Former Vice President Joe Biden, in an interview with the New York Times editorial board released Friday, conceded that his proposal to fix the healthcare system in the U.S. without transitioning to universal, government-run healthcare could still result in people losing insurance at the whims of their employer—remarks that progressives noted inadvertently helps make the case for the very Medicare for All plan Biden opposes.

“To use Joe Biden’s words—it’s a big f-ing deal that Biden was forced to explicitly admit to this enormous problem in his health care plan,” David Sirota, speechwriter for Biden primary contest rival Sen. Bernie Sanders (I-Vt.), said on Twitter.

To use Joe Biden’s words — it’s a big f-ing deal that Biden was forced to explicitly admit to this enormous problem in his health care plan https://t.co/ffULBjaHVC — David Sirota (@davidsirota) January 17, 2020

Biden was questioned on his pitch for a more modest healthcare plan involving the idea that Americans who like their private, employer-provided plans can keep them. Times editor Jeneen Interlandi pushed the former vice president on that claim, pointing out that such plans are subject to employers’ willngness to keep them in place.

“If you like your plan, you can keep it, assuming—I should add the obvious—if your employer doesn’t take it away from you,” said Biden.

“And with that, my friends, Joe Biden successfully makes the case for single payer healthcare,” tweeted activist Evan Sutton.

Progressive researcher Andrew Perez was among the first to seize on the remarks as an indication that any plan with less than universal coverage at its center—including today’s status quo—is insufficient.

“No one can promise to preserve your employer-based health insurance plan,” said Perez. “You lose it if you’re laid off, switch jobs, or if your employer changes offerings.”

The new Biden pitch: ‘If you like your private insurance, you can keep it, assuming your employer doesn’t take it away from you’ pic.twitter.com/65Xtvw2gNr — Andrew Perez (@andrewperezdc) January 17, 2020

RoseAnn DeMoro, former executive director of National Nurses United and an ally of Sanders, said on Twitter Biden’s admission exposes one of the key shortcomings of his entire approach to healthcare reform.

“Working people continually lose coverage from their employers,” said DeMoro. “The #1 cause of strikes is healthcare.”

The kind of system that Biden is proposing, warned DeMoro, doesn’t do nearly enough.

“This is exactly what we had before Trump,” she said, “and workers lost and lost and lost.”