Democrats have spent much of the past year piling up ambitious health care proposals, from single-payer to various riffs on the public option, that have often been criticized for being too expensive or politically unrealistic.

This week, they gave us a preview of their tepid fallback plan.

Not that they quite framed it that way. On Wednesday, Michigan Sen. Debbie Stabenow unveiled a bill that would let Americans ages 50 to 64 buy into Medicare—essentially creating a public option for the middle-aged, in which premiums would be set just high enough for the program to roughly pay for itself. The proposal is being backed by a wide array of Democrats, including a number of current and potential presidential contenders. Some of its supporters—such as Sens. Cory Booker, Kamala Harris, and Kirsten Gillibrand—have also endorsed Bernie Sanders’ Medicare for all bill. Others, such as co-sponsor Sherrod Brown, have said they prefer a more incremental approach. “I have always supported universal health care, but we are not there yet,” Sen. Tammy Baldwin, another co-sponsor, told reporters. “Medicare at 50 is a very bold step in the right direction.”

It would definitely be a step. But bold might be an overstatement.

The idea of letting Americans purchase Medicare coverage before they turn 65 has been floating around Washington for decades now. Bill Clinton proposed a buy-in for 62-year-olds back in 1998, when he was deep into the triangulating small-ball period of his presidency. The concept surfaced again during the intense Obamacare negotiations of 2009, until Joe Lieberman snuffed it out. Hillary Clinton, ever a fan of medium-bore policy solutions, backed a buy-in for those over 50 during her 2016 presidential run. And Stabenow herself introduced a buy-in for 55-year-olds last year.

The main upside of the buy-in is that it could be cheaper than the coverage currently available on Obamacare’s exchanges, at least for people who currently earn too much to qualify for the health law’s subsidies. Medicare pays doctors and hospitals lower rates for their services than private insurers, and the government doesn’t have to worry about running a profit. So even if enrollees have to pay full-freight, it might still be more affordable than a Blue Cross Blue Shield plan.

This year, for instance, a 60-year-old earning $50,000 will have to pay an average of $12,190 for a benchmark silver plan. By comparison, the Congressional Budget Office estimated in 2008 that the government would have to charge $7,600 a year if it wanted to break even on a buy-in program. The magic number is almost certainly higher today, and it won’t necessarily be cheap, but it might be cheaper than the eye-popping prices some people now face on the exchanges.

There are at least a few other perks to the idea. Because it’s designed to be more or less deficit-neutral, the buy-in would by definition be a cheaper way to expand coverage for older adults than simply making private insurance subsidies more generous (and make no mistake—subsidizing private coverage is probably going to get very expensive in the coming years). It would also ensure that middle-aged Americans always had at least one option to buy coverage, even if private insurers pulled out of the market (it’s been a while since health care observers were worried about bare counties, but you never know).

But this all raises a question: Why limit the buy-in to 50-year-olds? If it’s designed to cover its costs, why not open the program up to 30-year-olds or 25-year-olds or 18-year-olds? Focusing exclusively on older Americans might have made some semblance of policy sense during the late ’90s, since the insurance market was essentially unregulated at the federal level, and insurers could still reject you for looking at their paperwork funny. Giving near retirees the option to purchase a Medicare plan was a straightforward way to guarantee access to insurance when it was often nearly impossible for them to buy. But thanks to Obamacare, nobody has to worry anymore about being denied outright by insurers, and Americans of all ages face similar problems when it comes to getting covered. Middle-class households that earn too much to qualify for subsidies often can’t afford to buy policies through the exchanges. And those who can afford a plan often face sky-high deductibles.

When I asked Linda Blumberg, a health policy expert at the Urban Institute, if there was any technocratic reason why you wouldn’t want to also offer a buy-in to younger Americans as well as the 50–64 demographic, she was blunt. “There’s no reason why you wouldn’t want to make that available for any age,” she said. Other experts I talked to suggested that limiting the rollout to older adults might make it marginally easier to test and design, though Blumberg suggested that wasn’t really the case. “The desire to peel off the 50- to 64-year-olds at this juncture seems more arbitrary and complicated than people understand,” she told me.

When I asked Stabenow’s staff about these questions, the answer I got was fairly unsatisfying. In an email, a spokeswoman told me: “Americans approaching retirement are most likely to see cost increases and lack of affordable coverage. Allowing them to buy into Medicare is supported by the public and is something we can do right now.”

It is true that older Americans see the highest prices on the exchanges. But they’re not the only people being priced out. It’s also true that a buy-in for the 50-and-up set is popular (77 percent approve, according to the Kaiser Family Foundation), but not much more so than opening up a version of Medicare to everybody (73 percent approve). And the medical industry won’t be any less opposed to a buy-in for 50-year-olds than it would be to a full public option for everyone. The hospital lobby, which doesn’t want to see payment rates to providers cut, has already come out swinging against Stabenow’s bill.

The idea that Congress could pass a buy-in “now,” meanwhile, is just baffling. Stabenow’s staff told me she believes her bill can get bipartisan support (she’s said the same to Vox). And maybe she could get a friendly word from Susan Collins—who knows? But does she really think she could rally enough Republicans to overcome a filibuster? Does she believe that there’s a soft, social democratic heart beating beneath Mitch McConnell’s stern shell? After every bruising health care battle we’ve seen over the past decade, we’re still placing our hopes on bipartisan compromises? Seriously?

In the end, the main thing animating this bill seems to be a misplaced preoccupation with optics—an unmerited belief that taking a tentative baby step toward a full public health insurance option for all Americans will arouse less opposition than the real thing, while letting Democrats pass a bill they can technically describe as Medicare for more. It’s nice that an idea once considered too edgy to pass the Senate is now regarded as the incremental half-measure for moderate squishes. But it’d be a tragic missed opportunity if a future president didn’t aim their ambitions higher.