By contrast, Medicare does have effective tools for restraining prices, which is a major reason Medicare for All has gained ground. But universalizing Medicare isn’t the only way to tackle the affordability crisis. Lots of rich countries have multiple health plans and sensible pricing. To achieve this, however, requires major changes that the Affordable Care Act, for all its value, didn’t deliver.

First, there have to be much higher standards for all health plans, so they provide broad benefits without shifting costs onto patients. Second, these plans should cover everyone — not just because losing coverage is the ultimate affordability crisis (as we’re tragically learning), but also because universal coverage facilitates uniform, reasonable pricing. Third, there has to be a plausible way of financing this high-standard coverage as its reach broadens and costs rise.

Which brings us to the biggest prerequisite for success: power to push back on prices. If expanding Medicare is the route to broader coverage, then Medicare needs the reach and authority to rein in costs — for drug prices and medical devices as well as doctor and hospital charges. The alternative is a cycle of disappointment, in which gains in the breadth and generosity of coverage are continually undermined by skyrocketing prices.

In short, how you design the public option matters. You have to get people in it, and give it the authority needed to push back against an increasingly consolidated delivery system.

We can see these differences if we compare Mr. Biden’s proposal with the most ambitious public option plan offered during the campaign: the “transition” plan proposed by Elizabeth Warren after she backed away from an immediate leap to Medicare for All. Her transition plan is itself a more robust version of a public option proposal introduced in Congress by Representatives Rosa DeLauro and Jan Schakowsky (which, full disclosure, I helped design).