Former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE’s campaign is attacking Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) for saying he does not need to release details on how to pay for "Medicare for All" right away, part of an escalating battle over the issue in the Democratic presidential primary.

“It’s alarming that Senator Sanders, who has been up-front for years that Medicare for All would require middle class tax hikes, won’t tell voters 'right now' how much more they will pay in taxes because of his plan,” Biden deputy campaign manager Kate Bedingfield said in a statement. “If not now, then when?”

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She was responding to Sanders’s

comments to CNBC,

in an interview published Tuesday, when Sanders downplayed the need to release details on how to pay for his signature health care policy.

“You’re asking me to come up with an exact detailed plan of how every American — how much you’re going to pay more in taxes, how much I’m going to pay,” Sanders said. “I don’t think I have to do that right now.”

He said he did want the proposal to be paid for and would do it in a progressive way.

Biden, in the more moderate wing of the party, has been sparring with his progressive rivals, Sanders and Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.), over their support for Medicare for All.

Warren, by contrast, says she plans to soon release a plan for paying for Medicare for All, and she was not mentioned in the Biden campaign’s statement.

“When you’re running to take on the most dishonest president in American history, Senator Sanders and others who back Medicare for All have to preserve their credibility,” Bedingfield said.

Multiple studies have found Medicare for All would cost about $32 trillion over 10 years. Sanders has previously released financing “options,” such as a 7.5 percent payroll tax on employers, that together add up to about half of the projected cost.

Sanders and Warren both argue that middle-class people would end up saving money because their premiums and deductibles would be eliminated, more than balancing out the increase in taxes.

“At the end of the day, we will pay for every nickel of Medicare for All, and it will save the overwhelming majority of the American people, who will no longer pay premiums,” Sanders told CNBC.

Biden is instead pushing for building on ObamaCare by adding an optional government-run health insurance plan, rather than a mandatory one.