CONCORD, N.H. -- Sen. Bernie Sanders didn’t win the 2016 Democratic presidential nomination. But the self-proclaimed democratic socialist arguably accomplished a more lasting feat.

He changed the conversation – bringing one-time fringe positions like a "Medicare-for-all" single-payer health care system, a massive increase in the national minimum wage, and free tuition at community colleges and some public schools into the mainstream of the Democratic Party’s agenda.

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Now, his own success in shaping that agenda has raised an obvious challenge: He's no longer the only candidate in the field who stands for these issues. In fact, he's one of many.

Crystallizing this conundrum, the senator this week re-introduced an updated version of his Medicare-for-all bill and was quickly joined by four of his rivals for the nomination -- with Sens. Cory Booker of New Jersey, Kamala Harris of California, Kirsten Gillibrand of New York and Elizabeth Warren of Massachusetts all co-sponsoring.

It was the latest example of how, as the independent senator from Vermont runs a second straight time for the Democratic presidential nomination, he's both leading the charge on these policies but also fighting to stand out in a field of nearly 20 candidates, many like-minded.

For the time being, polling suggests primary voters are enthusiastic about the original purveyor of these proposals. He consistently rates at the top of the field alongside former Vice President Joe Biden, who has yet to jump in. Sanders himself is quick to remind voters he was the one promoting these ideas before they were so popular.

“I want to offer a very special thanks to the people of New Hampshire. In 2016, this is where the political revolution took off. Thank you, New Hampshire,” Sanders said in March as he returned to the first-in-the-nation primary state for the first time since declaring his 2020 candidacy.

Recalling his marathon primary battle against Hillary Clinton, he said, “the ideas that we were talking about then were considered by establishment politicians and mainstream media to be ‘radical’ and ‘extreme’ -- ideas, they said, that nobody in America would support.”

He highlighted that thanks to the wave that nearly carried him to the nomination, “those ideas that we talked about four years ago that seemed so very radical at that time -- well, today, virtually all of those ideas are supported by a majority of the American people and have overwhelming support from Democrats and independents. And they're ideas that Democratic candidates all across the board are supporting.”

Medicare-for-all is a prime example. A January poll by the Kaiser Family Foundation – which focuses on health care polling – indicated that 81 percent of Democrats supported a single-payer insurance model. That support dropped to 53 percent for independents and 23 percent among Republicans questioned. On Capitol Hill, meanwhile, support remains limited, with Democratic Leader Chuck Schumer stopping short of endorsing it.

SANDERS' PROPOSALS NOW EMBRACED BY 2020 DEMS

Sanders said his mission in the 2020 election is “to turn our vision and our progressive agenda into reality.”

But that mission is also the goal for many of his rivals for the Democratic nomination.

Sen. Warren, another politician popular on the left, is also pushing the same progressive proposals. And some of the other leading 2020 candidates – such as Sens. Booker of New Jersey and Harris of California, former Rep. Beto O’Rourke of Texas, and South Bend, Indiana Mayor Pete Buttigieg – are promoting similar plans, from criminal justice and immigration reform to refusing contributions from super PACs, corporations and lobbyists to battling climate change.

And some of those rivals are years younger than the 77-year-old Sanders and don’t carry with them a ‘socialist’ target on their backs.

Former Democratic National Committee Chairwoman Donna Brazile says that while Sanders does face a lot of competition in the progressive lane for the nomination, “they don’t have the same name ID as Hillary Clinton and the same type of broad support that Clinton had” in 2016.

“I do believe this is Senator Sanders' opportunity – his last opportunity on the national level – to score a major victory. This is about delegates, not popularity,” explained Brazile, a Fox News contributor.

SANDERS SAYS FELONS BEHIND BARS SHOULD BE ABLE TO VOTE

It’s early in the 2020 cycle – we still have 10 months to go before the voting begins – but so far Sanders has kept other candidates from stealing his thunder.

He surged out of the gate following his Feb. 19 announcement, drawing large crowds and racking up big bucks. Sanders hauled in $18.2 million in fundraising in the first 41 days of his campaign.

The senator consistently registers in second place in double digits in 2020 polling, trailing Biden – an all-but-certain White House contender – but ahead of the rest of the field.

And even though they have plenty of candidates to choose from this time around, many of his supporters are sticking with Sanders.

New Hampshire Sanders supporter Lorna Wakefield, who came in person to see Sanders in March when he returned to the Granite State, said she’s sticking with the senator 100 percent.

“Bernie’s the one who started this all. We’re with Bernie,” she said.

And, Chris Liquori – a member of the Sanders steering committee in New Hampshire – argued, “Why settle for the imitation when you’ve got somebody who’s been doing this for 40 years, who brought the party to its knees and brought them where they are now? Why would you go with anyone else?”