When Sen. Elizabeth Warren released her long-awaited plan for implementing universal health care on Friday, skepticism that her plan goes too far was to be expected from the Democratic presidential campaign’s centrist lane. But two days after the Massachusetts senator dropped her $20.5 trillion roadmap to universal health coverage for all Americans, the man who arguably injected the concept of “Medicare for All” into the party’s political mainstream said that Warren’s plan doesn’t go far enough.

“I think the approach that we have, in fact, will be much more progressive in terms of protecting the financial well-being of middle income families,” Sen. Bernie Sanders told ABC News on Saturday, alleging that Warren’s proposal could have a “very negative impact” on middle-class job creation.

“I think we have a better way, which is a 7.5-percent payroll tax, which is far more I think progressive, because it’ll not impact employers of low wage workers but hit significantly employers of upper income people,” added Sanders, who last week told CNBC’s John Harwood that he would not release a plan outlining how to pay for his proposal.

Former Vice President Joe Biden, meanwhile, who has lambasted universal Medicare coverage as unfeasible, accused Warren of lying about the bill being funded without tax increases on the middle class.

“She’s making it up,” Biden told PBS NewsHour after the plan was released. “There is no way.“ (The data regarding the funding for Warren’s proposal was collated by former Obama-era head of the Centers for Medicare and Medicaid Services Don Berwick and former Obama-era labor economist Betsey Stevenson.)

The two-sided pushback—coming from the author of the first legislation that would expand Medicare to cover all Americans and from the former veep who helped shepherd the Affordable Care Act through Congress—puts Warren in the increasingly familiar territory of having her policies simultaneously bashed as impractically liberal by centrist Democrats and insufficiently progressive by Sanders and his supporters.

“ A proposal like this would be lucky to get 20 Senate votes—it’s not a question of abolishing the filibuster or the machinations of Mitch McConnell. ” — Dr. Harold Pollack, a professor at the University of Chicago focusing on public health and health policy.

Warren, who described her proposal as grounded in the “radical idea” of “calling out what’s broken and speaking plainly about how to fix it,” countered that Biden was “running in the wrong presidential primary,” and said that Sanders’ critiques ignored that “not a single person who makes less than a billion dollars has to pay one penny in additional taxes.”

Speaking to reporters on Sunday, Warren said that she and Sanders “are heading in exactly the same direction” of eliminating the estimated $11 trillion Americans will pay in out-of-pocket medical costs over the next decade. “Bernie and I are out there for strengthening America’s middle class. I love it.”

Warren’s plan promises to pay for universal health care coverage with a wealth tax, increased taxes on corporations, and redirecting roughly $9 trillion in employer contributions for employee health insurance toward the government program.

“Health care is a human right, and we need a system that reflects our values,” Warren said in a statement accompanying the plan. “That system is Medicare for All.”

Warren’s plan does have its supporters on the left, including Rep. Pramila Japayal, who tweeted that the financing outline “shows we can spend less & cover everyone w/guaranteed, comprehensive care,” as well as health care activist Ady Barkan, who called the proposal an “enormous win.”

But beyond attacks from Warren’s rivals for the Democratic nomination was a wary reception by Democrats on Capitol Hill, who now openly worry that the issue is dead in the water legislatively—and could make it easier for Republicans to paint Democrats as too extreme to govern in the meantime.

“I’m not a big fan of Medicare for All,” House Speaker Nancy Pelosi told Bloomberg, adding that she wanted Democrats to keep one thing in mind: “Remember November.”

Dr. Harold Pollack, a professor at the University of Chicago focusing on public health and health policy, called the increasing support for such plans among Democratic presidential candidates a “heartbreaking mistake” for the party, both on political and policy grounds.

“ A proposal like this would be lucky to get 20 Senate votes—it’s not a question of abolishing the filibuster or the machinations of Mitch McConnell ,” Pollack, who has called on lawmakers to build on the Affordable Care Act rather than scrap it entirely, told The Daily Beast. “ From a political perspective, there are so many reasons why it’s not politically feasible. From a policy perspective, there are a million details that we have to both negotiate and also learn as we go if we’re trying to do some sort of a very major reform.”

Even the creation of a public option, as has been advocated by Biden and South Bend Mayor Pete Buttigieg, is “going to be a knife-fight,” Pollack said. “That’s gonna be itself a monster fight, but at least it’s a monster fight over something that could be accomplished.”

Kathleen Sebelius, who led the Department of Health and Human Services under President Barack Obama and helped implement the Affordable Care Act, told The Daily Beast that she found it interesting that Warren and Sanders “ don’t seem to be dismayed at all by the fact that it will be very very difficult to pass one piece of big legislation” in the notoriously fractious Senate, much less all of the sweeping changes to the health, financial, and energy systems that they have promised.

“We will not get to 60 Democrats,” Sebelius said. “So let’s say we have 51, 52, 53 Democrats, and you can get rid of the filibuster. Then I think you are in at least the ballpark of getting some major legislation through. But is that climate? Is it getting money out of politics? Is it changing the tax bill so that you actually have some revenue? Is it Medicare-for-All?”

“To have the two senators on the forefront of saying we can do these 20 things all at the same time, really sets up an opportunity for failure,” Sebelius said.

Warren, however, appears to have anticipated these critiques of a plan that would amount to sweeping changes to the health care, insurance and pharmaceutical industries.

“You know, a lot of people are afraid of big structural change,” Warren said at the Liberty and Justice Celebration in Iowa on Friday, after multiple rival campaigns had already put her plan on blast. “Afraid because they’re already rich and powerful and they may lose influence. Afraid because they’ve built lives sucking up to those who are rich and the powerful. Afraid because they see an America where they won’t be able to make the changes they need. Afraid because they are either too cynical or too downtrodden to believe that change is possible. Well, not me.”