For decades, Democrats have been the party of health care. Yet right now, presented with one of their greatest opportunities in many years to make the system more fair, expansive and affordable, they’re locked in a battle over which parts of their health-care agenda to leave on the side of the road.

A big and morally fraught conflict is shaping up between two major priorities: First, expanding Medicare benefits to include dental, vision and hearing treatment, and second, extending Medicaid coverage to people in 12 Republican states still refusing the Affordable Care Act’s expansion of the program.

The first is important to House progressives, and the second is a big goal of many other Democrats, including House Speaker Nancy Pelosi (D-Calif.), who are also championing expanded ACA subsidies. Though many in each group favor both, negotiations among Democrats over President Biden’s Build Back Better reconciliation bill might force one to be jettisoned.

This is presenting brutal choices that could impact tens of millions of Americans. And this is largely a creation of two senators: Joe Manchin III (D-W.Va.) and Kyrsten Sinema (D-Ariz.), who have demanded a dramatic reduction in the bill’s cost that seems rooted in arbitrary ideological opposition to government spending entirely divorced from the trade-offs this will require.

Sinema seems to want to jettison the provision allowing Medicare to negotiate lower drug prices. That provision would save hundreds of billions of dollars — which could fund the other goals. Manchin wants the cost down to $1.5 trillion, apparently because more generous spending will instantly transform us into whatever he means by an “entitlement society.”

Meanwhile, Politico reports that the conflict is intensifying in the House, with some centrists joining in opposition to expanded Medicare benefits. Like Manchin, they want such benefits means-tested, which would cut millions of Medicare beneficiaries out and impose a punitive new layer of bureaucracy to weed out the allegedly undeserving.

Progressives are drawing a hard line against throwing out those benefits. At the same time, as NBC reports, the House Democratic leadership seems most focused on the ACA provisions, including closing the Medicaid coverage gap.

To illustrate how terrible these choices are, we asked Larry Levitt, executive vice president for health policy at the Kaiser Family Foundation, to help calculate how many people would lose out from eliminating each big policy from the final bill.

Levitt says 62 million seniors and others could potentially benefit from expanding Medicare to cover dental, vision and hearing treatment. So enormous numbers of people might lose out if this were jettisoned.

Meanwhile, Levitt estimates that in the 12 states that have not expanded Medicaid, there are around 2.2 million people in the so-called coverage gap, which means they’re just above the threshold to qualify for traditional Medicaid but don’t earn enough to qualify for ACA subsidies.

That’s far fewer than would lose out if Medicare were not expanded. But here the dilemma deepens: Those in the Medicaid gap may arguably be in more serious need. The vast majority are concentrated in southern states — Florida, North Carolina, Georgia and Texas — and expanding Medicaid would give them access to a range of health-care benefits they currently lack.

“These are all poor, uninsured adults,” Levitt told us. “Fifty-nine percent are people of color. The Medicaid gap is not only the biggest hole in the ACA; it also raises fundamental questions of equity.”

“Health care for seniors or health care for poor people is a difficult trade-off for Democrats,” Levitt added.

What’s frustrating is that Manchin and Sinema have not offered serious explanations for why their demands for less spending are worth sacrificing these other priorities to achieve. Because they’ve managed to keep the debate at a deliberately opaque level of abstraction — less spending good, more spending bad — the human toll of the trade-offs here is largely absent from the discussion.

“The spending number is one way of measuring the legislation’s reach, but it completely obscures the human impact,” Jonathan Cohn, author of a history of the ACA, told us. “Every one of those dollars goes to a program that addresses a specific need, whether it’s poverty level families who need basic health coverage or seniors who can’t pay for dental care.”

“Cost matters,” Cohn continued, “but so should the cost of inaction.”

All this is a vivid demonstration of just how complicated the task of governing can really be — for Democrats, that is.

When in power, Democrats try to address thorny problems such as the lack of affordable child care or the deficiencies in our health-care system, problems that lack simple solutions and demand extremely complex policy design. Solving them often requires overcoming entrenched, wealthy interests, and hinges on the grueling, years-long process of implementation.

And for Republicans? Their response to needs such as child care, health insurance or family leave is “Who cares?” If it can’t be fixed with a tax cut for the wealthy, they won’t bother.

The Build Back Better bill is big and complicated, because it seeks to address so many problems at once. We won’t know for years just how successful it was. But it’s already clear that even if it passes Congress, there will be a lot left to do — and many people left behind.

And Manchin and Sinema have made it so, for reasons they still haven’t truly explained.