The center of power in the Democratic Party is moving rapidly leftward and Sanders is serving as the conductor.

As Bernie Sanders deliberated his 2016 run for the presidency, he understood that his odds of toppling Hillary Clinton were low.

But winning was never the lone goal for the gruff independent from Vermont.

Despite more than two decades toiling in Congress, Sanders remained a backbench player, he confided to a top adviser at the time, according to "Shattered: Inside Hillary Clinton's Doomed Campaign." He sought a higher profile in the U.S. Senate for the liberal causes he had built his career around. A well-run White House campaign, win or lose, would do the trick.

Fast-forward more than two years and Sanders is seeing that notion bear fruit.

While his former primary opponent, Hillary Clinton, is relitigating the last war, an emboldened Sanders is already making moves to shape the next one. Clinton may technically be right, as she continues to assert in interviews, that Sanders "is not even a Democrat." But it's Democrats who are increasingly gravitating to Sanders, as 16 did this week by joining his legislation calling for a Medicare-for-all health care system.

Clinton is indicating she wants to remain active in politics by backing Democratic candidates in 2018 who can help flip Congress. But in a striking role reversal, it's the 76-year-old Sanders who now wields more power among the next line of budding aspirants in Democratic politics.

"This week looks like a moment where it's crystallizing in a lot of people's minds that Bernie Sanders is the future of the Democratic Party," says Mark Longabaugh, a Democratic consultant and aide to Sanders' presidential bid. "There's an assumption within the Democratic Party that a progressive candidate is a weakness. That's not a weakness, that's a strength. We have to lose some of the timidity that the party has had for too long on policy issues. How did Donald Trump end up as president? The public is restless and extremely unsatisfied with the performance of government. You have to make an argument. Put big bold ideas on the table. The public may not agree with every aspect, but they're going to give you credit for trying to do something. Bernie Sanders put it on the table and argued for it."

Just look at some of the names who stood next to him Wednesday to roll-out his universal health care pitch: Sens. Kirsten Gillibrand of New York, Elizabeth Warren of Massachusetts, Kamala Harris of California and Cory Booker of New Jersey.

All are prospective candidates for the presidency in 2020 – and 10 months following the party's harrowing 2016 defeat, they found themselves moving towards Sanders ideologically and physically, as each waited for his call Wednesday to make remarks at a Capitol Hill podium.

"I want to say thank you to Bernie for all that you have done," Warren gushed.

Their embrace of a single-payer position comes even as Clinton continues to tar the plan as unrealistic. But if that remains the majority position among Democrats, liberal activists don't think it will be for long.

"If you look at the list who are co-sponsoring this and those who are rumored to be interested in [the presidency], you see some alignment. I don't think that's a coincidence," says Kenneth Zinn, the political director of National Nurses United, a staunch supporter of the Sanders legislation. "This is how change happens. Grassroots action, bottom-up pressure. I think anyone who wants to be considered a progressive has to sign on to this bill. This is indeed becoming a litmus test for the movement."

When Sanders began crafting the bill back in the spring, his office reached out to senators they considered to be natural allies, as well as those with higher ambitions. After weeks of behind-the-scenes haggling over exact details, Harris, the freshman senator, endorsed the bill at the close of the summer congressional recess during a town hall in Oakland, California, dubbing it "a nonpartisan issue." The fact that her home state legislature wrestled with an ultimately unsuccessful universal health care endeavor helped move the needle.

Warren followed a week later, citing the GOP's persistent efforts to repeal the existing Obamacare program. "We owe a huge debt to President Obama," she wrote in an email to supporters. "But there's so much more we could do right now to bring down the costs of quality health care for every American."

Then came Gillibrand who said she'd be "fighting with Bernie", following her broad support for the concept during a Facebook Live event in June and Booker, who told a New Jersey television station on Monday "this is something that's got to happen," billing it as the next civil rights battle.

Even some alumni of the Clinton campaign acknowledge the winds are blowing in Sanders' direction.

"During the 2016 primary, Hillary Clinton understandably felt that she owed it to voters to only promise what she honestly felt she could deliver as president. But as Democrats engage in this post-2016 rebuilding, progressives appropriately believe it is important to make a statement on principle in favor of a Medicare-for-all system, regardless of the practical hurdles," says Brian Fallon, the national press secretary for Clinton's 2016 campaign. "I would bet many Democratic candidates running in the midterms may, for now, hew towards some of the on-ramp style proposals, such as those offered by Sens. [Brian] Schatz and [Chris] Murphy, but anyone seeking to lead the party in 2020 should probably be wary of rejecting the aspiration behind Sen. Sanders' plan."

And Sanders' diehard supporters are watching – and they are keenly aware of who isn't on board.

Winnie Wong, a co-founder of People For Bernie and an aggressive internet activist, targeted Democrats on Twitter who steered clear of the Sanders bill.

"If @ChrisMurphyCT is smart, he'll wake up in the AM, tell his staffer to draft a press release saying he'll be going with Bernie's bill," she wrote, targeting the Connecticut Democrat.

"Baby we got your number," she fired off to the account of Senate Majority Leader Chuck Schumer, including a link meant to pressure those not on board.

But in a sign of how far the debate had moved, even Sen. Joe Manchin, who faces a potentially competitive re-election challenge this year in increasingly conservative West Virginia, paid tribute to the legislation's concept if not its particulars.

"It should be explored," he told Bloomberg, later issuing a statement clarifying his skepticism about the merits of single-payer.

But Sanders' team is betting that the concept will gradually gain popularity as he crisscrosses the country in the coming months to promote it.

"I'm aware of at least one meeting in West Virginia of Trump supporters, people who voted for Trump, and when asked if they supported single payer, half the hands went up," says Jeff Weaver, a political adviser who ran Sanders' presidential campaign. "This approach has broad-based support among working class, middle class people, small business people, medical professionals, really across partisan lines."

What's unclear is if Sanders will harness his skyrocketing influence around other issues, like a $15 minimum wage and his plan for free college tuition.

Longabaugh sees the trend as inevitable.

"Look at the number of people standing with him. [New York Gov.] Andrew Cuomo standing with Bernie Sanders for free college tuition," he said, referring to their joint appearance in January.

"[Clinton] can talk about registration labels. But when they were in the Senate at the same time, Bernie Sanders voted with Democratic leadership more than Hillary Clinton did."

Sanders himself may decide to run for president again, but regardless of his personal decision, he's setting an early bar of what constitutes a true progressive in the era of Donald Trump.

Whereas in 2016 the assumed risk was to be positioned too far to the left of Clinton, heading into 2020, the hazard appears to fall too far to the right of Sanders.