The new plan from Senator Bernie Sanders needs a tax policy not just to fund it, but to dictate how it works.

With the support of 15 congresspeople and significant grassroots and poll support, the bill is unprecedented, both in the scope—it would in essence nationalize one-sixth of the largest economy in world history—and in seriousness. Although the initiative is almost certainly doomed over the course of the next few iterations of Congress, it’s now a rallying point, one its creators and sponsors aim to make the center of Democratic policymaking for years to come.

The broad strokes of Medicare for All are simple enough. Sanders’s plan would completely replace the existing patchwork of employer, exchange, and public insurance—save for Veterans Affairs and the Indian Health Service—and replace them with a plan that covers, well, everything. Medicare for All would cover doctor visits, specialty care, inpatient visits, drugs, home care, and mental-health services, while also taking care of vision and dental benefits. Save for a provision allowing some limited cost-sharing for prescription drugs, all of those services would be covered with no cost-sharing—no deductibles, copayments, or coinsurance—whatsoever. Additionally, the plan bars private insurers from providing “health insurance coverage that duplicates the benefits provided under this Act,” and would slowly expand to edge those insurers out of the market over the course of four years.

What takes shape over the 96-page document isn’t really a scaled-up Medicare program, but something new altogether. As currently constructed, Medicare actually contains quite a bit of cost-sharing—particularly for prescription drugs—and an entire industry of private plans exist to beef up Medicare coverage and provide additional services for seniors. Sanders’s plan would more accurately be described as The U.K.’s NHS on steroids—a entirely government-backed endeavor bounded only by the limits of the delivery system and of the tax base that pays for it all.

But that last point is crucial. Especially in a system with no artificial or individual limits on how people can use their health insurance, the funding structure is absolutely vital to understanding how the system as a whole will respond to the health-care choices of over 300 million people. And beyond the “how will they pay for it?” criticisms from both Republicans and Democratic holdouts, for all American health-care reforms—especially one this massive—questions of redistribution, the minutiae of tax policy, and how those economic factors shape and alter behaviors and health-care choices are important. In fact, those questions are as important in understanding if the policy actually meets the goals of covering people and containing costs as the specifications of Medicare benefits. And the Sanders plan, as of yet, answers none of those questions.

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Tax policy and the funding structure matter for each of those. They aren’t ancillary concerns; rather, they affect the nuts and bolts of how the policy works. It’s not just about where the money comes from, but from whom it comes and how. Health and wealth are intricately connected. Health policy is tax policy.

That’s why the Medicare for All bill as it stands is fundamentally incomplete; an unknowable quantity. Again, some of that is by design—the legislation won’t pass and the document serves mostly as a way to gain consensus on the vision. But while relegating the less sexy, and much more controversial funding elements to the background is perhaps politically pragmatic, putting it off can only hurt the policy in the long run. For example, it’s possible that somewhere in the foreseeable future, politicians, now enamored with the idea and bound by their pledges to Medicare for All, could pass it with a largely unsubsidized VAT, passing many of the consumption costs onto the poor people the program is meant to help.

Given the vision of Medicare for All as a paradigm that breaks the inequalities central to American medicine, it follows that the paradigm’s funding can’t reinforce those inequalities. Ensuring the progressive vision means ensuring every cent is accounted for up front, and that the costs and mechanisms of managing those costs are known. In order to meet its desired potential as a policy that reshapes the country, the Sanders plan still has plenty of work to do.