With Elizabeth Warren’s plan to fund “Medicare for All” in the news, the Hill decided to ask a few Democratic senators whether they’d support it. They were not enthused.

Alabama’s Doug Jones, who will probably need a divine intervention to win reelection in his crimson-red state, said he is a no. So did New Jersey’s Bob Menendez, who fell back on the popular line that he didn’t want “to take away private insurance from the union members who have worked so hard to negotiate for it.” But maybe the most damning comment came from Maryland’s Ben Cardin, who suggested that single payer probably wouldn’t even get a vote in his chamber.

“I don’t know that we’ll have a chance to do that; I think we’ll take up our own proposals,” he said. “I’m for universal coverage, I’m for building on the Affordable Care Act. My preference is to move forward on a public option.” If Democrats controlled the Senate, he added, “I think we would look to build on the Affordable Care Act,” rather than pass Medicare for All.

Cardin’s comments are especially weighty because, ideologically, he falls smack-dab in the middle of his party’s Senate caucus. If you want a feel for what a normie Dem has to say on the issue of health care, Cardin’s your guy. He also sits on the finance committee’s health care subcommittee, which means he’d personally have some hand in shaping almost any legislation the party tried to move.

So too, of course, would House Speaker Nancy Pelosi, who’s lately been trying to tamp down all the single-payer talk. Here she was recently in Bloomberg:

Pelosi said Democrats should seek to build on Obamacare instead of pushing ahead with the more sweeping Medicare for All plan favored by Warren and Sanders that would create a government-run health insurance system and abolish private coverage. “Protect the Affordable Care Act—I think that’s the path to health care for all Americans. Medicare For All has its complications,” Pelosi said, adding that “the Affordable Care Act is a better benefit than Medicare.”

This is what makes the whole conversation about Medicare for All so surreal. On the primary trail, Warren and Bernie Sanders are trying to outdo one another over who has the best plan to nationalize the American health insurance system. Journalists and think tankers—myself included—are scrutinizing the detailed mechanics of their proposals while the candidates’ supporters snipe at one another. Just about every primary debate has started with a repetitious scuffle over single payer. The topic has sucked the oxygen out of almost any other major policy discussion.

Meanwhile, the people in Congress who would need to support any actual legislation are saying over and over again that it’s never going to happen. And they are almost certainly correct. Even if Democrats can retake the Senate—which would require a small miracle—there is more than enough opposition to kill a single-payer bill. Sitting Sen. Amy Klobuchar is campaigning for president on a platform that consists largely of trashing Medicare for All. Ohio’s Sherrod Brown, long one of the chamber’s most progressive members, says that it would be a “terrible mistake” for the Democratic nominee to support Medicare for All. Joe Manchin exists. Kyrsten Sinema exists. These are the facts on the ground. And while Bernie Sanders can threaten moderates like Manchin all he likes, American presidents don’t exactly have the greatest track record of bending a recalcitrant Congress to their wills, even when they’re relatively fresh off an election win and Capitol Hill is led by their own party. (See: Donald Trump and Obamacare repeal, George W. Bush and Social Security privatization, Bill Clinton and his health care plan.)

So why are we even talking about Medicare for All at this point?

One part of the answer is that presidential campaigns aren’t just about making realistic promises about what you’ll do in the White House, but are also about laying out a broader philosophical vision. They are also a chance to change public opinion: Single payer was barely on the public’s radar before Bernie Sanders ran in 2016. Now it’s mainstream. And while Sanders and Warren might have little chance of passing Medicare for All as president, their efforts to build support for it could pay off one day down the line when President Alexandria Ocasio-Cortez is entering her first 100 days in office. It’s fair to think about all this as part of a larger, ideological battle over the party’s very long-term future, not just on health care policy but regarding the entire size and role of government in society.

Ezra Klein articulated another reason we’re so focused on this thing that probably won’t happen, arguing in a very good article in Vox that what we’re really witnessing is a debate over political tactics, two clashing theories of change. The left believes that if it demands a full loaf on health care, then it might eventually get half once it comes time to pass a bill. The moderates, on the other hand, worry that if a Democratic president pushes for something too extreme on health care in 2021, nothing at all will pass. Warren and Sanders are trying to avoid a repeat of Obamacare, which was consciously designed as a compromise with conservatives and was watered down further as it progressed through Congress. The moderates are trying to avoid a repeat of the early 1990s, when Bill and Hillary Clinton’s health care push ended in total collapse.

But there’s an additional, possibly more cynical layer of this whole odd debate. Warren is fighting to win over Sanders voters (or at least trying to make herself acceptable to them) and has pretty clearly decided that hugging single payer for dear life is the only way she can do it. Early on in the campaign, she was wishy-washy on health care. It wasn’t really her issue. When Bloomberg’s Joe Weisenthal asked her in January whether she’d support banning private insurance or preferred something more like a public option, she basically answered: Yes, all of the above.

Weisenthal: But right now, your vision for Medicare for All, would it all be a public option, or would it also include private insurance? Warren: So right now, there are multiple bills on the floor in the United States Senate. I’ve signed on to Medicare for All. I’ve signed on to another one that gives an option for buying into Medicaid. There are different ways we can get there. But the key has to be always keep the center of the bullseye in mind. And that is affordable health care for every American.

Warren got raked by the online left for answers like this. And within six months, she’d changed her tune, declaring “Yes, I’m with Bernie on Medicare for All” at a debate. I have no idea if she is or isn’t a true convert on the issue. But her position on single payer has definitely evolved and hardened through the campaign.

But while she’s trying to court left-wing primary voters, Warren obviously also has an eye on the general election. Sanders has been content to tell voters he will raise their taxes to pay for single payer but lower their health care costs. Warren clearly sees this line as a political loser and so has pieced together a $20 trillion plan that does policy acrobatics to avoid an explicit middle-class tax hike.

This is the tension largely keeping the single-payer debate at the center of the campaign. A serious Democratic contender is lashing herself to a policy that’s symbolically essential to the left while trying with all her might to make it palatable (or at least not a complete deal breaker) to the center, and it’s unclear whether she’ll succeed. Add to that the lack of support among important legislators in her own party and you get an odd policy spectacle that gives journalists something to talk about, even if the idea is DOA in Congress.