Democratic presidential hopefuls Vermont Senator Bernie Sanders (L) and former Vice President Joe Biden chat during a break in the fourth Democratic primary debate of the 2020 presidential campaign season co-hosted by The New York Times and CNN at Otterbein University in Westerville, Ohio on October 15, 2019.

Joe Biden's presidential campaign, raising questions about Bernie Sanders' "credibility," ripped his 2020 rival for declining in a CNBC interview to say how he'd finance 'Medicare For All.'

"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," deputy campaign manager Kate Bedingfield said in a statement.

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

The Biden campaign was reacting to Sanders' statement in a CNBC Speakeasy interview that he felt no need to spell out a complete financing plan for Medicare For All, which analysts say will cost $32 trillion over 10 years. Sanders has offered $16 trillion worth of options so far, while noting that federal taxes already pay for large chunks of the plan's ultimate expenses through the existing programs including Medicare and Medicaid.

"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 during the interview, conducted last week in Des Moines, Iowa. "I don't think I have to do that right now."

"At the end of the day, we'll pay for every nickel of Medicare for All," the self-styled democratic socialist continued. "It will save the overwhelming majority of the American people, who will no longer pay for premiums."

"At the same time we are learning that Joe Biden has a Super PAC to bankroll his campaign with unlimited donations from corporations and billionaires, he is once again peddling dishonest insurance company talking points about Medicare for All," responded Sanders campaign manager Faiz Shakir. "Biden's proposal preserves the corporate greed and corruption that rots our health care system, and his plan leaves millions of Americans uninsured.

"Will Joe Biden tell the American people how many more of them he's willing to allow to go bankrupt? How many more people would die because they don't get to a doctor in time? We need to have the guts to stand up to corporate greed. That's what this election is about."

Sanders was articulating a more politically cautious position than fellow progressive Elizabeth Warren, another Medicare for All advocate who has built momentum in the race all year. Under pressure from rivals for vagueness in a recent debate, Warren now says she is preparing a detailed plan for covering the enormous cost of the proposal.

Building his nomination bid around support from more moderate Democrats, Biden has proposed a more limited health coverage expansion. He would preserve the private insurance plans covering most Americans while allowing those uninsured to purchase a Medicare-style "public option."

The former vice president says the new revenue to pay for his proposal would come from higher taxes on drug companies and investor profits, not on the middle class. That approach fits his contention — affirmed in current national polls — that he holds the strongest chance of defeating President Donald Trump in next November's general election.

Biden is not the only prominent Democrat challenging statements from Sanders in the CNBC interview.

Asked whether conservative Democrats such as Sen. Joe Manchin of West Virginia would back his far-reaching plans such as Medicare for All and the Green New Deal, Sanders replied "damn right they will." He explained that as president he would travel to West Virginia to rally working-class voters to apply pressure and overcome Manchin's resistance.

Manchin, whose coal-dependent constituents remain strongly behind Trump, swiftly disputed Sanders.

"Bernie is damn wrong," Manchin told NBC's Frank Thorp.