During the 2016 primary campaign, eventual Democratic presidential nominee Hillary Clinton derided discussion of her primary opponent's single-payer health care plan as "a theoretical debate about some better idea that will never, ever come to pass."

Oh, how the times have changed for Sen. Bernie Sanders.

The Vermont independent is releasing a new "Medicare for All" bill on Wednesday, and instead of it being subjected to dishonest smears from the Democratic establishment, it has instead received the support of a cadre of mainstream party members, many of whom are already seeing their names appear in the same sentence as "president" and "2020." And that says a lot about what Democrats think of the 2016 election and how they intend to approach policy going forward.

"What this struggle is about really, honestly, is not a health care debate. Should health care be guaranteed to all people? Most people say yes. Are we wasting an enormous amount of money in the current system? Most people would say yes," Sanders said in an interview with Vox. "Can we take on the drug companies and the insurance companies and Wall Street and their unlimited sums of money to influence Congress? That is another issue, and that's a major political struggle that we have to engage in."

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Indeed, a lot of this is about politics, but the details are also important. Under the plan, which Sanders' team has been releasing to various media outlets ahead of its official introduction, the age for Medicare – the single-payer program for Americans 65 and older – would be gradually lowered over four years, while those under 18 would be included immediately. Eventually, just about everyone would be under Medicare's umbrella.

When it comes to cost, copays and deductibles would be eliminated on everything but prescription drugs, and vision and dental care care would be covered. The Veterans Affairs health system and the Indian Health Service would be preserved for those who use them.

Private insurance wouldn't be totally eradicated, per se, but it would only be used to cover supplemental stuff like plastic surgery that is deemed medically unnecessary. The bill won't explicitly lay out which taxes will necessarily be raised to cover the cost, with Sanders saying that will be worked out in future legislation.

Signing on are with Sanders are Sens. Elizabeth Warren, D-Mass., Kirsten Gillibrand, D-N.Y., Cory Booker, D-N.J., and Kamala Harris, D-Calif., considered 2020 contenders all, along with several other members of the Democratic Senate caucus. In the House, there's been a similar stampede to cosponsor Rep. John Conyers', D-Mich., longstanding single-payer bill.

A fringe idea, then, this is not, which is quite a change from previous years in which Sanders found no sponsors for his single-payer efforts. In a world in which a reality television actor can become president of the United States, perhaps anything is possible.

As I noted a couple of weeks ago, when it comes to health care, Sanders is winning the long game, making single-payer a de facto part of the Democratic platform. Back in 2008, no Democratic presidential hopeful endorsed the idea, as it was thought to be so impossible that it wasn't worth considering; come the next election, they all might. There's little chance the rush to back single payer would be occurring were it not for Sanders having gone the distance against Clinton last year.

Sure, a lot of the surge in single-payer sponsorship reeks of political opportunism, since endorsing an idea is cheap and easy when the other guys control Congress and the presidency. Elected Democrats have a tendency to love some truly progressive ideas only when there's no way of implementing them.

But creating this sort of momentum behind an idea, however it happens, is also the whole point of engaging in politics. For whatever reason, be it policy conclusions or electoral convenience, big name Democrats now see it as better to be for single payer than against it; Sanders proved that there's a lot to be gained from embracing big, progressive solutions to national problems, and now others are following in his wake.

So support begets support, which begets legislative language and policy debates and better ideas, until something that was once thought a pipe dream is perhaps someday bearing the signature of the president. And even if it doesn't ever become law, it creates momentum and space for other ideas that could achieve true universal health care coverage. That's how change happens.

Conservatives, of course, are blowing a gasket about the increasing support for single payer, condemning it as the arrival of dread socialism on our shores. But the concept itself, depending on how you ask the question, is pretty popular, as are the government-run health care programs like Medicare and Medicaid that the right loves to hate. Perhaps the constant labeling of everything to the left of a Heritage Foundation white paper as "socialist" has inoculated the public a bit to that particular charge?

And look: If everything Democrats do on health care is going to get called socialist anyway, no matter how incremental or market-friendly it is, they might as well go all in on single payer. Politically, they're facing the same heat either way.

Plus, anyone who has interacted with our kludgy, often impenetrable health care system knows full well that private insurance companies are no sympathetic players looking out for the well-being of the average American, deserving of sympathy when Big Government runs them out of business. They're headache-inducing at their best and downright evil at their worst. It's no surprise folks are open to an alternative system entirely.

Of course, the real test of the staying power of single payer as a policy idea will come when Democrats have power of their own again in Washington. Then, they will have to decide if they want to spend political capital navigating the many thorny issues regarding actually passing and implementing what is now mostly rhetoric. It's not like getting single-player into law would be a light lift.

And, today notwithstanding, I'm sure we have not seen the end of Democrats whining about Sanders having a pernicious effect on the party because he or his supporters are undermining its precious unity. There are almost certainly going to be spats over whether support of single payer, or any other Sanders priority, should be a litmus test for Democratic hopefuls in the 2018 midterms and beyond.