Bernie Sanders’s health-care plan, which he released hours before Sunday night’s Democratic Presidential debate, under the rubric “Medicare for All,” is a remarkably ambitious effort, proposing as it does to replace the current mix of private and government insurance with a single-payer system. Yet the accompanying document devoted to explaining how the plan would work, and what it would mean for patients and providers, consists of just a couple of pages. Considering that Sanders wishes to bring about nothing less than a complete transformation of the U.S. health-care system, that seems a tad skimpy.

Of course, the document’s purpose is primarily political, so you could argue that it’s more important for Sanders to lay out his broad vision there than to get into specifics. The problem is that, when you’re talking about the health-care system, God (or the devil, depending on your perspective) is very much in the details. Moving to the kind of single-payer model that Sanders envisions would require a host of difficult choices. It would demand dramatic changes in the way that health-care providers of all kinds do business, and in the way patients get care.

Take the question of cost. Although the plan is called Medicare-for-All, in fact it’s much more generous than Medicare. It would give all Americans dental, vision, hearing, mental-health, and long-term care, massively expanding both the number of people who have insurance and the range of treatment they can get. It would also eliminate co-pays and deductibles. “As a patient, all you need to do is go to the doctor and show your insurance card,” the plan says. All things being equal, these changes would significantly increase the amount that Americans spend on health care (currently around three trillion dollars a year). Yet the plan also calls for trillions of dollars less to be spent on health care over the next ten years. In other words, Sanders is promising more coverage and more treatment, for a dramatically lower cost. How would he pull this off?

The answer in the document is vague: “Reforming our health care system, simplifying our payment structure and incentivizing new ways to make sure patients are actually getting better health care will generate massive savings.” The general idea seems to be that moving to the single-payer model will lead to a huge drop in administrative costs, and will also allow the government to use its leverage to drive down the prices of drugs and medical devices. According to an analysis that the campaign released by Gerald Friedman, a professor of economics at the University of Massachusetts at Amherst, costs in the new system would also rise much more slowly than they do today. Sanders claims that, all told, his plan will save ten trillion dollars across ten years.

Neither the plan nor Friedman explains where those ten trillion dollars would come from. “The pleasure of being an academic is I can just spell things out and leave the details to others,” Friedman told the Times. “The details very quickly get very messy.” A study he published in 2013 of a single-payer plan that was introduced in the House by Representative John Conyers, of Michigan, suggests that Friedman is assuming a single-payer system would save almost five hundred billion dollars in administrative costs, by eliminating the huge bureaucracy now devoted to billing- and insurance-related issues. Cutting prescription-drug spending would save another hundred and twenty billion or so. But even if you accept these estimates as realistic (plenty of observers would not), where are the rest of the savings, approximately four hundred billion dollars a year, going to come from? The best the campaign can offer is a vague reference, in Friedman’s analysis, to “a slowdown in the growth of spending.”

The truth is that if you want to save a trillion dollars a year in health-care spending, you can’t do it solely by cutting administrative costs and drug prices. You have to be willing to spend far less on medical procedures and services, and to be far more rigorous about expenditures for new medical technology. That would probably mean a drop in income for some doctors, particularly high-priced specialists, as well as for many hospitals. Providers would also have to relinquish a great deal of control over their facilities and equipment.

Indeed, a proposal for a single-payer system made by Physicians for a National Health Plan, the organization that has done perhaps the best work studying how to make such a model cost-effective, calls for the complete abolition of for-profit hospitals, and places the responsibility for managing “health facilities and expensive equipment purchases” in the hands of regional planning boards. Sanders’s initiative would almost certainly require something similar, but he says nothing about what will happen to hospitals. In fact, the word “hospital” doesn’t even appear in his plan. This might be politically sensible, since talk of government planning boards deciding whether or not your hospital gets a new MRI machine would undoubtedly make some people nervous. But it’s not exactly forthright.

The Sanders plan also makes it sound as though Americans would never again have to worry about not having coverage for some treatments, or about not being able to see their preferred doctors. “Patients will be able to choose a health-care provider without worrying about whether that provider is in-network and will be able to get the care they need without having to read any fine print or trying to figure out how they can afford the out-of-pocket costs,” it says. If a single-payer plan is to hold down costs, though, the government will have to make choices about paying for some things and not for others, which necessarily means that some treatments people really want won’t be covered. Indeed, a footnote in Friedman’s analysis acknowledges that his figures assume that twenty per cent of people’s projected out-of-pocket costs would be for things found to be “not medically necessary.” Similarly, a single-payer plan, if it is to keep costs down, would have to limit how much it would pay doctors, which would likely mean excluding from the system those who won’t accept lower fees. In that event, some patients would no longer be able to see the doctors they wanted. (The plan generally fails to discuss the thorny question of whether people will be able to get health care outside of the single-payer system, either by purchasing supplementary insurance or paying doctors directly, as they do now with physicians who don’t accept their insurance.)

The point isn’t that a single-payer system is a bad idea, per se, nor even that it’s wholly unrealistic from a political perspective. Rather, it’s that Sanders needs to be more forthright and detailed about what his plan would entail, and specifically about the fact that it would require major and often unwelcome changes not just for businesses that many people dislike, such as insurance and drug companies, but also for doctors and hospitals, which are generally popular. And he should acknowledge that the single-payer model would, in some cases, mean big and potentially controversial changes for patients, too. Moving to a single-payer system would be a tumultuous experience, and it’s a proposal worthy of a great deal of open debate. Sanders can certainly make a case that such a transition would be beneficial, given the enormous amount of waste and inefficiency in our current system. But he needs to stop pretending that it would be easy.