WASHINGTON — Battle lines are sharpening on health care for 2020 Democrats, with former Vice President Joe Biden and Sen. Bernie Sanders, I-Vt., kicking off the most high-profile fight yet on the topic among the field's top-tier candidates.

On the one side is Biden, who is making the case that Democrats should retain the core structure of the Affordable Care Act, which subsidizes private insurance and Medicaid for Americans who don't get coverage from their employer or other government programs.

On the other is Sanders, who has long called for guaranteeing every American coverage through a more generous version of Medicare and banning competing private plans.

"There's a lot of people that don't want to give up their private insurance and their employer-based insurance," Biden said on MSNBC's "Morning Joe" on Tuesday. "They'd have a choice to keep it. And so I'm prepared to debate that. I'm anxious to have that debate. That's a legitimate difference we have between me — and where apparently everyone from Kamala to Bernie to Elizabeth are."

On Monday, Biden released a $750 billion plan to repair holes in Obamacare, expand subsidies for insurance, and add a new public option customers could purchase instead of private plans.

He paired it with a stinging rebuke of proposals like the Sanders bill, effectively portraying them as a personal attack on President Barack Obama (who, for his part, has said some vaguely positive things about "Medicare for All"). In recent days, Biden has decried single-payer Medicare for All as too costly, citing Sanders' debate concession last month that it would require new taxes on the middle class, and too disruptive, noting it would abolish existing private plans.

"Starting over makes no sense to me at all," Biden said in a video announcing his plan. "I knew the Republicans would do everything in their power to repeal Obamacare. They still are. But I'm surprised that so many Democrats are running on getting rid of it."

Sanders, the author of the leading single-payer health care bill in the Senate, is set to deliver what the campaign is calling a "major address" on Medicare for All on Wednesday.

In a possible preview, the Vermont lawmaker ripped Biden on Sunday for criticizing his plan, saying his rival's remarks left the false impression that Americans would not have access to care. Sanders accused Biden of parroting conservative talking points, saying he "would hope that my fellow Democrats would not resort to misinformation about my legislation."

While health care is an issue that the entire Democratic field often weighs in on, the debate between Biden and Sanders stands out from the rest because of the candidates' policy plans, personal history and political message.

Among the five top-polling candidates nationally, Biden is one of two, along with South Bend, Indiana, Mayor Pete Buttigieg, running on a plan to build incrementally off the ACA. Three others (Sanders, Sen. Elizabeth Warren, D-Mass., and Sen. Kamala Harris, D-Calif.) are backing the same single-payer Medicare for All bill. Neither Warren nor Harris were in the Senate when the ACA passed, while Biden played a public role in advancing it to passage.

All of this makes Biden a natural foil for Sanders, who holds a unique position in the field as the nation's most prominent advocate for single-payer health care.

While Warren and Harris support the Sanders bill, neither have made it central to their campaign. Until recently, it wasn't clear that Warren considered it part of her platform while Harris has sometimes seemed uncomfortable discussing features of the legislation.

That's left it to Sanders to take the lead in this policy dispute — a role he seems eager to embrace.

"We cannot continue to tinker around the edges while 80 million Americans lack health insurance or are underinsured with high premiums, copays and deductibles," Sanders said in a statement last weekend responding to Biden.

While much of the field has discussed a public option in general terms, Biden's plan goes into more detail than most, making it a strong jumping-off point for debate. Sen. Michael Bennet, D-Colo., who has his own bill to create a "Medicare X" option, said he was "glad that (Biden's) digging in the same place we are."

The Biden proposal is essentially a list of targeted responses to common complaints about Obamacare in the decade since its passage:

For those who make too much money to qualify for government subsidies, which now cut out for customers with incomes over 400 percent of the federal poverty level, the bill expands them to everyone on the ACA exchanges and caps contributions at 8.5 percent of income.

For those who find deductibles are too high on Obamacare plans, it provides subsidies for a more generous tier of plans.

For those who don’t like their insurance choices, it adds a public option based on Medicare.

For those caught in the "Medicaid gap" in states that didn't expand the program, it provides access to the new public option with zero premiums.

Sanders, on the other hand, is set to offer the opposing case Wednesday: Rather than keep adding new features to the existing mix of private and public insurance plans, the government should step in and cover almost everyone under one government plan with no premiums or deductibles.

Without the government assuming the mantle of the nation's primary insurer, he's argued, too many uninsured Americans will fall between the cracks and industry groups will have too much leverage to raise premiums and charge more for drugs and hospital services.

"We believe that health care is a human right and we are going to fight for a system that is based on human needs, not corporate profits," Sanders said Monday in Philadelphia promoting a plan to use federal funding to purchase failing hospitals.

While the Sanders plan represents the party's left flank in the debate, Biden's proposal also reflects the party's movement on health care since the ACA debate, when moderate and conservative Democrats killed plans for a public option.

Among other features, the plan includes a now-common Democratic proposal to allow Medicare to negotiate lower drug prices, requires its public option to cover abortion, and opens up the ACA to undocumented immigrants, while barring them from using taxpayer subsidies to buy insurance.

Underscoring the challenge either plan would face in Congress, a coalition of major health industry groups opposed to Medicare for All denounced the former vice president's proposal Monday.

The plan "would undermine the progress our nation has made and ultimately lead our nation down the path of a one-size-fits-all health care system run by Washington," Lauren Crawford Shaver, executive director of The Partnership for America’s Health Care Future, said in a statement.