Joe Biden and Bernie Sanders traded unusually personal shots concerning their disagreements over "Medicare-for-all," with Biden's team saying Sanders lacks "credibility" on the issue -- and Sanders' campaign returning fire by suggesting Biden is dishonest, corrupt, and willing to let Americans go bankrupt or die.

The spat underscored a divisive issue facing the winnowing, leftward-drifting field of Democrats seeking to unseat President Trump in 2020. Elizabeth Warren, who has been rising in the polls, has dodged questions as to what tax increases would be needed to support Sanders' plan for universal health coverage, which she supported.

"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 Wednesday.

She added: "When you're running to take on the most dishonest president in American history, Sen. Sanders and others who back 'Medicare-for-all' have to preserve their credibility."

IT DOES NOT APPEAR 'MEDICARE FOR ALL' CAN BE FUNDED BY TAXING THE RICH, STUDY SHOWS

At a town hall in Iowa before a crowd of approximately 175, Biden took another shot at Sanders.

"Unlike a lot of people, I tell you what my plan costs," Biden said. "It won’t cost $3.4 trillion a year. It will cost somewhere between $600 billion total, to $720 billion. That can be funded with the present tax system. It’s a one-shot thing. You can buy in."

The comments came after Sanders remarked in a CNBC interview that he did not feel compelled to explain exactly how much "Medicare-for-all" would cost. The Committee for a Responsible Federal Budget (CRFB), a bipartisan budget watchdog, released a report Monday detailing options for how the federal government could pay for the roughly $34 trillion the plan would require -- and its findings showed there would be no way to fund the expanded health program simply by raising taxes on the rich.

Sanders' campaign wasted no time in shooting back at the remarks from Biden, noting that Biden's team has had to turn to super PACs because it's been struggling financially.

"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,'" Sanders campaign manager Faiz Shakir said in a statement. "Biden's proposal preserves the corporate greed and corruption that rots our health care system, and his plan leaves millions of Americans uninsured."

BIDEN DENIED COMMUNION OVER STANCE ON ABORTION

Shakir added: "When we eliminate premiums, co-payments, deductibles and out-of-pocket expenses, the overwhelming majority of people will pay less for better health care. 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."

"Will Joe Biden tell the American people how many more of them he’s willing to allow to go bankrupt?" — Sanders campaign manager Faiz Shakir

The role of middle-class taxes in funding "Medicare-for-all" has become a point of contention in the primary, and it showed at the most recent debate in Ohio. Warren tiptoed around questions from the moderators about whether or not middle-class taxes would increase under her "Medicare-for-all" plan. Warren chose to focus on net costs instead.

"I will not sign a bill into law that does not cut costs for middle-class families," she said.

South Bend, Ind., Mayor Pete Buttigieg, who has endorsed a public option plan rather than Warren's single-payer "Medicare-for-all," accused her of being evasive.

"Your signature, senator, is to have a plan for everything — except for this," he said. "No plan has been laid out to explain how a multitrillion-dollar hole in this 'Medicare-for-all' plan that Senator Warren is putting forward is supposed to get filled in."

Sanders, who has been fond of reminding Democrats endorsing "Medicare-for-all" that he "wrote the damn bill," was more open than Warren about his plans to finance the $30 trillion health care plan.

"It is appropriate to acknowledge that taxes will go up," he said. "For virtually everybody, the tax increase they pay will be substantially less than what they were paying for premiums and out-of-pocket expenses."

A 32-percent payroll tax increase would bring the rate to 47 percent on most wage income, according to the CRFB report. A 25-percent income surtax would force the lowest federal income tax rates to 35 percent and compel the top earners to pay 62 percent of their income.

The options for financing "Medicare-for-all" without increasing taxes would be similarly immoderate. The CRFB said the federal government would need to cut "non-health federal spending by 80 percent" in order to pay for "Medicare-for-all" without increasing taxes. That likely would require cutting Social Security benefits from approximately $18,000 to about $3,600 each year and cutting troop numbers from 1.3 million to 270,000.

If a Warren or a Sanders administration decided to finance "Medicare-for-all" simply on debt, consequences could be dire, according to the report.

"Deficit-financing 'Medicare-for-All' would be far more damaging to the economy," the report said. "Assuming that such a massive increase in the debt would not roil financial markets or lead to high inflation, we estimate that a 108 percent of GDP increase in the federal debt would shrink the size of the economy by roughly 5 percent in 2030 – the equivalent of a $4,500 reduction in per-person income – and far more in the following years."

The report also acknowledged the best way to finance "Medicare-for-all" might be to make the plan less ambitious than progressive leaders like Sanders and Warren have proposed.

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"While the financing options above are quite large in magnitude, they could be reduced significantly by reducing the cost of 'Medicare-for-All' itself," the report said. "These cost reductions could be achieved in part by reforming or reducing provider payments, improving care coordination, and identifying policies to reduce excessive utilization of care."

Fox News' Madeleine Rivera and Tyler Olson contributed to this report.