“We’re addressing it on both ends,” Mr. Sanders said. “We’re addressing it now by trying to help the people who have past due medical bills. And we’re addressing it by finally creating a health care system that guarantees coverage to people without any premiums, without any deductibles, without any out-of-pocket expenses.”

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Medical debt affects Americans who lack health insurance, of course. But it is also increasingly affecting people who have insurance with holes, like high deductibles or limited networks of doctors whose care is paid for. Around 16 percent of adults with credit reports have at least one medical debt, according to a study published last year in the journal Health Affairs.

The plan calls for the government to negotiate and cancel the debts, though it does not specify the precise mechanism.

While eliminating every American’s medical debt would probably not come cheap, Mr. Sanders’s plan could wind up costing far less than the total amount of debt he is seeking to cancel. Craig Antico, a founder of the charity RIP Medical Debt, which buys and forgives medical debt, estimated that the market price for $81 billion in debt could be as low as $500 million. Most past-due medical debt never gets paid, which is why bill collectors are often willing to sell the debts for pennies on the dollar.

The plan would also create a public credit rating agency to “replace” for-profit companies like Equifax, and it would exclude medical debts from credit ratings. It would establish a new legal process, managed by the bankruptcy court system, to help adjudicate medical debts that are not yet in collections.