What Bernie Sanders' Progressive Backers Say He Accomplished During His 14-Month Presidential Campaign

— -- Bernie Sanders is expected to endorse Hillary Clinton at a joint event in New Hampshire later this morning, almost a month after the last votes in the Democratic Party’s primary were cast.

The Vermont Senator won 22 states, received more than 12 million votes, and guaranteed that Clinton campaigned for the nomination until the very end. During interviews with ABC News, Sanders’ biggest backers said they were confident that the senator’s prolonged candidacy, and refusal not to bow out even weeks after Clinton became the party’s presumptive nominee, would not dent his legacy.

“It is hard for me to take that kind of talk seriously. We’re talking about a political establishment that has never once understood Bernie Sanders or the movement,” Charles Chamberlain, Executive Director of Democracy for America, told ABC News. “Sanders understands the movement he is leading and he knows that he needs to make sure that our people are going to show up to the polls in November. We need to have the time to work with the Clintons to get the party platform changes that we need and heal from the primary before we just flip a switch.”

When asked to reflect on what the lasting legacy of the Sanders campaign might be, the senator’s first congressional endorser, Arizona’s Raul Grijalva, got a little teary-eyed. “A little bit of passion, a lot of emotion and chipping at the rock,” he said of his colleague. “It behooves our party to understand that you can’t poll-test sincerity and it behooves our party to understand that you can’t super-PAC sincerity.”

Challenging Clinton

Ahead of the event today, the Clinton campaign offered concessions to Sanders and his fans in the form of two major updates to her policy platforms on health care and college affordability, coming closer to his proposals on each. In addition, over the weekend, the Democratic Party finalized a progressive platform agenda, which included several proposals from the Sanders campaign.

"Whether or not he should have supported Hillary sooner rather than later will be debated, but soon forgotten," Vermont Congressman Peter Welch said. "The impact that he has had is already felt in the democratic platform. In fact, Hillary Clinton is quite wise, because she largely embraced rather than disputed his agenda."

Over the course of the primary, Clinton altered or solidified her position in order to match Sanders on a number of issues from opposing the transpacific partnership and the Keystone pipeline, to supporting a $15/hr federal minimum wage in some areas, expanding social security, and taking on big banks.

"Although he lost the nomination he may have won the argument in the party and in the broader public," said Anna Galland, Executive Director at MoveOn.org.

Galland argued that Clinton’s responsiveness to the senator’s ideas was in her long-term political interest. "It makes it more likely that young voters and other Bernie supporters will rally strongly around Bernie’s campaign," she added.

New Fundraising Model

Sanders also challenged the idea money from special interests or deep-pocketed donors was necessary to run a national campaign.

"How successful he has been at getting new people in politics, managing to accomplish it without big super PACs, is sort of a model for the future," Welch continued.

"Both the form and content of his campaign have changed what future campaigns must look like," Galland echoed.

The underdog progressive ran on the idea that corporate money was hurting American politics and refused a super PAC. According to his campaign and filing disclosures he raised almost $225 million and received more than 8 million contributions, most of them small, averaging around $27 apiece.

He often called his fundraising "revolutionary."

He Got the Kids to Care (a lot of other people too)

Exit polls from primaries and caucuses show Sanders won an astonishing 71 percent of voters under 30 years old nationwide. He also consistently won with independents and brought new voters to the polls. In Iowa, for example, Sanders won 59 percent of first time caucus-goers.

Galland said she hoped that part of Sanders’ legacy would be a "hope that people-powered politics is still possible."

"We are capable of doing more -- doing more in politics where volunteers educate and inspire other voters and move millions of people to participate in the political process," she added.

Inspiring the Next Generation of Politicians

"I think we are going to see literally thousands and thousands of Bernie supporters running for key offices within the democratic party, completely reform the party, and I think we are going to see Bernie revolution candidates in 2018, 2020," Chamberlain continued.

Chamberlain noted that his organization, which was started after Howard Dean’s failed bid for the White House, was "never anywhere near the size of the movement that Bernie Sanders put together," but was still helping to elect their members 12 years after Dean’s run.

According to the Sanders campaign, over 15,000 people expressed interest on their website in running for office after the senator said last month said he hoped to continue his movement by backing progressives around the country and encouraging his supporters to run.

"We have built this massive infrastructure of people across the country who are going to continue to fight and work for change," said Larry Cohen, former president of the Communications Workers of America and who has been working with the senator’s campaign.

Looking Under the Hood of the Party

By competing in every Democratic primary contest, Sanders directed the national spotlight onto election rules and preparedness in each state, from Nevada caucus rules to long lines in Arizona, and six-month early registration deadlines in New York. He also inspired a robust conversation about the role of the party’s super-delegates. Having performed better in open primaries, where independents as well as registered party democrats could vote, the senator and his fans have pledged to continue to fight for rule changes like automatic voter registration and open primaries going forward.

"I think we will look back on this on this election and see our party, as democrats, being more democratic, being more progressive and being more decentralized,” Grijalva continued. “We are going to look back and say Bernie started this."