Sen. Bernie Sanders (I-Vt.) plans to unveil a new version of his “Medicare-for-all” proposal on Wednesday. But the actual substance of the plan may matter less than what he says about it ― and the role he envisions that proposal playing in future debates over how to reform the U.S. health care system.

He could try to make it a litmus test, by presenting his proposal as a near-finished piece of legislation and demanding that Democrats pledge fealty to its particulars. Or he could present it more as a concept, something he expects progressives to spend the next few years refining, with a greater emphasis on the goal of truly universal coverage than the specific means for achieving it.

The former approach sounds bolder. The latter could ultimately do more to make health care available and affordable.

Certainly Sanders has earned the right to talk about Medicare-for-all. He’s among a small group of public officials who have been pushing the idea literally for decades, no matter what the political climate. And if he hadn’t made the concept such a prominent part of his 2016 presidential campaign, nobody but a handful of relatively low-profile progressives would be talking about it now.

Instead, Democratic senators are lining up to co-sponsor his bill, including four (Cory Booker of New Jersey, Kirsten Gillibrand of New York, Kamala Harris of California and Elizabeth Warren of Massachusetts) who are potential Democratic presidential candidates for 2020. An even more unexpected endorsement of the concept, if not the Sanders proposal specifically, came last week from Max Baucus, the relatively conservative former Democratic senator from Montana who was a key architect of the Affordable Care Act.

The resurgence in interest makes sense. The Affordable Care Act has helped millions to get insurance, improving access to care and offering financial security many lacked before. It also created a political consensus behind the essential principle of universal coverage ― that everybody should have insurance, regardless of income or medical condition.

But the law has also fallen short of realizing that goal. Millions of Americans still don’t have insurance. Millions who do are stuck with high premiums or out-of-pocket expenses. The new system seems to have particular trouble in more rural parts of the country, where sparse populations make it difficult for private insurance markets to thrive. That’s why Republicans have been able to get as far as they have with their repeal effort ― and why even Democrats are talking about how they’d like to improve the system.

Sen. Bernie Sanders (I-Vt.) plans to unveil a new version of his “Medicare-for-all” proposal Wednesday.

Sanders has made clear his preference, and on Wednesday he’ll offer the latest version of it when he formally unveils his new plan. Chances are it will look a lot like the one he proposed during the 2016 campaign. That would mean calling for the federal government to create a new insurance plan that would supplant existing insurance arrangements, including the private coverage people get from employers.

The benefits would be comprehensive, including all medically necessary treatments, with little or no out-of-pocket expenses. In this respect, the term “Medicare for all” is a bit misleading. The insurance he has is in mind would be considerably more generous than what the government now offers seniors ― again, assuming he hasn’t strayed too far from what he was promising last year.

To finance the new system, people would have to pay new taxes, in lieu of the premiums they now pay on their own or indirectly through employers. To make the whole system affordable, the government would have to exert some kind of control ― over the nation’s total health care budget, individual fees for the providers and producers of medical care, or both.

Versions of such a “single-payer” system already exist in a few countries around the world: Canada, Sweden and Taiwan among them. Coverage is truly universal in these places, because enrollment is basically automatic at birth, and financial hardship from medical bills barely exists. Overall, these countries spend far less on health care, which means they have more money left to spend on other things.

These systems entail their own trade-offs, like entrusting government to make more decisions about what to cover and how to pay for it ― and plenty of reasonable people…