The most intense policy debate going on in the Democratic Party right now concerns health care, but it’s about more than just what sort of specific reform should be pursued. It’s also about how to approach both policy and politics, about what it means to be a Democrat, and about competing theories of change.

Though at times it can get heated, there’s nothing wrong with that — Democrats argue passionately about this issue because they care about people who don’t have coverage and people who are ill-served by the system we have now. And though people both on the left and in the center can be dismissive of those who don’t agree with them, it’s important for everyone to understand exactly what others are proposing.

On Wednesday, four Democrats — Sen. Debbie Stabenow (Mich.), Sen. Tammy Baldwin (Wis.), Rep. Brian Higgins (N.Y.) and Rep. Joe Courtney (Conn.) — are unveiling a bill to allow anyone over the age of 50 to buy in to Medicare, which is currently open only to those over 65. This idea is a variant of one that has been around for a while; you may remember the failed liberal push for a “public option” in the Affordable Care Act.

But today, allowing people to buy in to Medicare if they want, and paying premiums to cover the cost, is just about the most widely popular health-care idea around. And those who prefer something approaching a single-payer system see it as an inadequate half-measure that doesn’t fix the basic problem with the system.

This week I spoke to Stabenow about this bill and the debate within the Democratic Party. Though in past years she had introduced similar bills allowing for a buy-in at age 55, she said that may no longer be sufficient.

“I’m seeing more and more people in my state who are in a situation where they’re being laid off at 52, 53, forced to take early retirement, people telling me that they’re holding their breath until they get to age 65," Stabenow told me. She also said she consulted with health-care economists who told her that it wouldn’t make a difference to the viability of a Medicare buy-in to lower the age. Quite the contrary; younger enrollees will on average be healthier and cost less to insure.

But she’s clearly attuned to the political risks that accompany even a seemingly moderate proposal such as this one, especially the disingenuous Republican argument that letting younger people access Medicare will threaten the benefits of current recipients. For that reason, Stabenow’s bill establishes a separate insurance pool for those age 50 to 64. The purpose is to be able to say to seniors that this is entirely separate from their Medicare, though that won’t stop Republicans from demagoguing the issue.

When I pressed Stabenow on how this proposal fits into a longer-term reform of the system, she resisted. “This could be a first step or it could be the place at which Medicare lands,” she said. “That has yet to be decided. But this is what I know: This is doable now.”

Which is fair enough. Huge numbers of people could benefit from a Medicare buy-in, and it would certainly be harder for Republicans to demonize.

By contrast, an overhaul of the entire system might be more politically treacherous.

“What do we do with folks that currently have negotiated a union contract and feel they have good insurance and don’t want to make a change?” she asked. “I believe strongly, and every single person in the Democratic caucus agrees, that health care is a basic human right, not a privilege. But the question is, within the system that we have in the United States, how can we make that coverage a reality?”

Even if you’re advocating a swift transition to a universal system, those are questions you have to grapple with. Thinking everyone will get on board with a more radical reform because it promises the best future is naive; people are very protective of what they have now, even if what they have now is inadequate.

And there’s a way to square the practical and the idealistic perspectives. What if you saw something like this 50-plus Medicare buy-in as a necessary step toward a universal system? Instead of hoping to overcome people’s loss aversion, make it work to your advantage by giving them more benefits and more options piece by piece, ratcheting up their expectations until a universal system becomes inevitable?

Though that’s not what Stabenow is trying to achieve, she’s aware of the dynamic. “We’ve now changed people’s expectations about health-care coverage,” she told me. Stabenow pointed to the public backlash to GOP efforts to repeal popular provisions of Obamacare, and said: “The expectations have changed and therefore the politics have changed.”

But there’s one more political obstacle even to a modest reform such as this one: the filibuster. So I posed to Stabenow a hypothetical: Let’s say it’s 2021, Democrats have taken back the White House and the Senate, her bill has majority support in both houses, and the only thing standing in its way is the filibuster. Would she support getting rid of it? After criticizing Senate Majority Leader Mitch McConnell’s (R-Ky.) profligate use of the filibuster, she said that it’s what makes the Senate different from the House (and all senators look with scorn on the House). Here’s where she ended up on that question:

I don’t support on policy removing the filibuster. However, as a member of the Budget Committee I will say that when we pass a budget resolution we can give authority for two reconciliation instructions that only need 51 votes to move forward on a policy, and that’s certainly something I would support doing for health care.

There will be many on the left who disagree and who believe that getting rid of the filibuster is essential to passing genuine reform in all kinds of areas. That’s another debate Democrats will and should have. But we should know by know that no matter how they go about it, every reform Democrats attempt will run into huge resistance and require a long and difficult fight with Republicans. Whatever approach you favor, you can’t pretend to be serious unless you have a plan to win those fights.

Read more:

Paul Waldman: On health care, Democrats aren’t messing around

Catherine Rampell: Democrats in 2020 are at risk of turning into Republicans in 2016

Robert J. Samuelson: Don’t expand Social Security. Our elderly are mostly fine.

Carter Eskew: Medicare-for-all? Without action, there won’t be Medicare at all

Paul Waldman: If you want Medicare-for-all, prepare for a long and bloody fight