Bernie Sanders sealed Medicare for All’s place in the popular imagination with his 2016 presidential run. Ever since, its popularity has continued to grow: multiple recent polls show that 70 percent of Americans support the single-payer policy, which would cover all American residents through a comprehensive, national insurance plan.

This is bad news for establishment Democrats, who have a vested interest in maintaining the market-based system we have today. In an attempt to counter Medicare for All, they’ve rallied around a less radical approach that will preserve the private insurance industry and keep their donors happy — the “public option.”

The public option is a pretty self-explanatory idea: basically, the government would allow people to “buy in” to public health insurance, whether that be through Medicare, Medicaid, or a public plan on the Affordable Care Act market. Proponents of the public option love to argue that people are happy with their private plans, and that what they really want is — in the words of Tim Kaine — “more choices, not less.”

This is a dishonest reading of public opinion. While polling shows that as many as 71 percent of workers say they are “satisfied” with their employer-sponsored insurance — this is in a country where the alternative is having no insurance at all. In reality, nearly everyone is anxious about healthcare coverage and in search of healthcare security.

The Medicare for All bills in the House and Senate would provide us with that security by guaranteeing equal, comprehensive coverage to all American residents through a single, public program. Public option plans, on the other hand, would compete against private insurers in our current broken, market-based system, ultimately perpetuating the unequal coverage, underinsurance, and prohibitive out-of-pocket costs we see today.

It’s no mystery why top Democrats are scared of Medicare for All. Its massive popularity among their voters puts them in an awkward position with their donors. By crowding the field with half-measures, they thus hope to confuse the debate and allow themselves wiggle room to maintain their cozy relationships with insurance industry executives.

Beyond the shady reasons for its existence as a legislative proposal, the public option is simply bad policy. Unlike single-payer, the public option won’t get rid of out-of-pocket costs; it won’t give us freedom of choice in doctor and hospital; and it won’t divorce healthcare from employment, leaving millions tied to jobs they hate just so they can keep their insurance.

But here’s the key thing — it won’t be universal.

The greatest political strength of single-payer is its universal coverage. By covering every American and eliminating private alternatives, single-payer carries a massive built-in constituency. This means that, like social security, once it’s in place it’s going to be very difficult to erase.

The public option has no such political guarantees. By adding some people to a public plan while leaving millions under private insurance, the public option would carve up the constituency it would need in order to remain politically viable. Fragmented approaches to healthcare breed envy, resentment, and scapegoating. On the other hand, universal approaches engender solidarity.

If we want health reform that survives non-stop attempts to dismantle it, everyone needs to benefit from the legislation. This way, everyone has a stake in guaranteeing its continued existence. It’s why our motto has always been everybody in, nobody out.

As Medicare for All becomes increasingly viable, our main fight as advocates is to prevent it from being watered down into — or outright replaced by — a public option plan. This is no easy task, given that we’re up against the entire democratic establishment while also dealing with nonstop right-wing attacks. But we have to remain vigilant. Healthcare will never be truly universal until we eliminate financial barriers to care and cover everyone with a single, public program. The public option isn’t going to get us there.