(CNN) Vermont Sen. Bernie Sanders on Wednesday defended his "Medicare for All" bill against escalating attacks from critics like former Vice President Joe Biden, while also challenging the Democratic primary field to reject donations from private health insurance and pharmaceutical interests.

"If we are going to break the stranglehold of corporate interests over the health care needs of the American people, we have got to confront a Washington culture that is corrupt, that puts profits ahead of the needs of the people," Sanders said in a speech. "That is why today I am calling on every Democratic candidate in this election to join me in rejecting money from the insurance and drug companies. Reject that money."

Sanders' call capped off a contentious week that saw Biden unveil his own health care proposal , which would greatly enhance Obamacare's subsidies to help people by coverage and create a public insurance option. During the rollout, Biden leveled attacks -- some of them misleading -- against Medicare for All and what a transition to a single-payer program would mean for people covered under the existing system. Biden's comments added fuel to a long-running debate in the Democratic Party, and among its presidential candidates, over how to expand government-backed coverage while most Republicans continue to seek its demolition.

Speaking at George Washington University, Sanders -- without naming Biden -- also lashed out at the "half-truths, misinformation and in some cases outright lies that are being spread about Medicare for All."

"Medicare for All critics tell us that Americans just love their private health insurance companies," Sanders said as the friendly audience laughed along. "You know what? I have never met one person who loves their insurance company. I have met many people who do love their doctors and their nurses who have very good experiences in their hospitals. And what we do is to say you can go to those doctors, you can go to those hospitals, but you're not going to have to anymore deal with ripoff insurance companies."

Aides to Sanders and Biden scrapped on Twitter ahead of the Wednesday speech, after the Sanders campaign accused Biden of lying in his recent remarks about Medicare for All and how it would affect people currently on programs like Medicare.

"Biden absolutely did lie when he echoed Donald Trump's lies by telling seniors' @BernieSanders will throw them off Medicare -- and Biden should now have to explain himself," Sanders speechwriter David Sirota tweeted.

That prompted a response from Biden spokesman Bill Russo, who posted a screencap from a piece of the bill and added, "Section 901 of the Medicare for All Act lays it out: Medicare, Medicaid, and CHIP as they exist today go away. Defend your replacement all you want, but the bill pretty clear that existing federal health programs go away. Biden told the truth."

The Biden camp was correct in the most narrow terms -- those programs, "as they exist today," would indeed "go away." But people covered through them would be insured through Medicare for All. Seniors would actually get better benefits than they have now from Medicare since Sanders' plan would also provide vision, dental and hearing aids and would eliminate all premiums and out-of-pocket costs.

The "pledge" Sanders introduced during the speech asks that Democratic presidential candidates "refuse to knowingly accept any contributions over $200 from the PACs, lobbyists, or top executives of health insurance or pharmaceutical companies." Donations from "rank-and-file" industry employees would not come under scrutiny.

Sanders gave a preview of his Wednesday comments -- and a widening effort to hit back against Biden -- a day earlier, when his campaign posted an interactive quiz on its website asking supporters if they could identify "who said it" about Medicare for All. The options -- underneath a series of six quotes -- included Biden, Trump, Senate Majority Leader Mitch McConnell and former President Barack Obama, whose praise for single-payer during a 2003 speech was featured in the final question.

The shots continued later in the day during a live-streamed video chat, when Sanders responded to Biden's suggestion last week that Americans risk "a hiatus" of months or years as officials push for Medicare for All, by saying he wanted "a health care debate on the facts and not on fear-mongering."

The two most recent editions of Sanders' legislation include a four-year transition period, which would go into effect only after the bill was signed and a process set in place. The current system would remain in place until that time, and Americans would join the government program in stages over the four years.

On Tuesday, Sanders argued that the duration of the phasing-in process was, in fact, cautious to the extreme.

"People are telling me that in the year 2019, after Medicare has already been around for over 50 years, when we have all kinds of technology, that somehow we really can't do it over a four-year period," he said. "And to answer the question, we're being pretty conservative here. I think it can be done quicker."

Sanders on Wednesday also asked whether the Democratic candidates in the field who say they support Medicare for All, including his four Senate colleagues who signed on as cosponsors, are prepared to unequivocally reject any significant future role for private insurers.

Massachusetts Sen. Elizabeth Warren raised her hand during a debate last month when the candidates were asked if they'd be willing to abolish the industry as part of establishing single-payer. New York Sen. Kirsten Gillibrand, who wrote the bill's transition plan, and New Jersey Sen. Cory Booker have said private insurers should not be shut out entirely.

California Sen. Kamala Harris' stance is less clear. She has insisted that Medicare for All would not completely wipe out the industry. But that is true only up to a point -- with the bill only leaving room for, as Sanders himself has said, private insurers to cover certain elective procedures, like cosmetic surgery.

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Asked on Tuesday what Medicare for All would translate to during a Harris administration, Harris told CNN her definition stated "that everyone will have access to health care and cost will not be a barrier."

"As it relates to private insurance, there will still be supplemental insurance, but transitioning into Medicare for All will at some point reduce the requirement for insurance, because everyone will have access to health care," the California Democrat said, though she warned it might take more than four years to complete the transition.

The role of those insurers, she added, would only be to "cover what is not otherwise covered."

Harris also said that she would not raise taxes on the middle class -- only on wealthier Americans and Wall Street -- to help pay for the program. The Sanders campaign has stated that tax hikes across the board would be required to make Medicare for All work, arguing that any added tax burden would effectively be canceled out by the elimination of health insurance premiums, co-payments and other out-of-pocket expenses.

On Wednesday, Sanders senior adviser Jeff Weaver rejected Harris' suggestion that single-payer could function without those broader tax increases.

"I mean, without unicorns, magic wands -- health care is not free," Weaver said. "There's doctors, nurses that have to be paid. There's hospitals. You have to have to pay for it. People will paying less under Medicare for All than they are now, and that's the point."