The details of the legislation give policy wonks a chance to dissect the latest version of an idea that Sanders has championed for years, though never with the kind of political support it has now. The measure sets up a national health insurance program administered by the federal government. Everything from primary care to hospital stays would be covered under the plan without a requirement for out-of-pocket spending on deductibles and copayments. Access to abortion is also included, which would effectively overturn the ban on federal funding for abortion known as the Hyde Amendment. And patients could still use private insurance programs to cover services deemed not medically necessary by doctors, like plastic surgery.

There is a caveat to the idea of no out-of-pocket cost in Sanders’s single payer system: The legislation gives the Health and Human Services secretary the ability to impose copays for prescription drugs as a cost-saving measure to incentivize the use of less expensive generic versions. The bill also promises to lower drug costs by calling on the government to negotiate prices with pharmaceutical companies.

Absent from the legislation is a detailed accounting of how the proposed single-payer system would be paid for. The legislation calls for the creation of a universal health insurance trust fund, and a bill summary mentions “changes in the Internal Revenue Code,” but doesn’t explicitly address the issue of what taxes might be imposed to cover the cost. On Wednesday, Sanders will outline potential ways to finance the plan, including the implementation of new, progressive taxes, as part of his single-payer push, through the specifics of those ideas won’t be included in the text of the legislation, according to an aide.

The United States spends more on health-care costs per capita than other industrialized nations. Implementing a single-payer system could bring down overall cost by eliminating inefficiencies, but a significant increase in taxes would prove controversial and could create a significant political obstacle to enactment.

A majority of Americans, at 58 percent, said the government has a responsibility to provide health coverage, according to a June survey by the Pew Research Center. But as my colleague Olga Khazan has reported, support for single payer decreased when people were told their taxes would go up. Republicans, meanwhile, have already started to attack single payer as an exorbitantly expensive idea.

The policy specifics, and the potential consequences, of Sanders’s single-payer legislation will be subject to intense scrutiny, from health-care experts and political opponents.

“The growing liberal enthusiasm for single payer has clouded the reality that the many formidable obstacles to its enactment have not disappeared,” Oberlander said. “One of those barriers to how to arrive at a politically viable way to finance the plan. Is Sanders going to offer a more realistic financing approach and accept other trade offs, such as benefit limits, or will this be a legislative utopia? Single-payer plans are easy to devise, at least in theory; they are much harder to enact.”