While he received more support from 18- to 29-year-old voters than all the other 2020 candidates combined, he only won 14 percent of the vote from those over 65. He carried the popular vote by only narrow margins in both New Hampshire and Iowa. And the fact that his signature issue is single-payer health care means that industry lobby will continue to work diligently to stop him.

"If I were in my old job in the industry, I would be freaking out,” said Wendell Potter, a former health insurance executive who now serves as president of the advocacy group Business for Medicare for All. “It’s going to be a huge fight. What we are beginning to see is the mother of all propaganda campaigns because the industry views this as the biggest threat it ever had.”

Throughout the campaign, Sanders has held town halls and asked voters to speak about their problems dealing with the health care industry. In the final days before the first-in-the-nation primary, he talked often about the opioid epidemic, a top issue in New Hampshire: One of his applause lines was when he said that drug manufacturers “hired more salespeople” when they realized their product was addictive.

“Even if people are not 100 percent on board with Medicare for All, what they hear in that is that the for-profit system is not working,” said Sara Nelson, president of the Association of Flight Attendants, of Sanders’ pitch for single-payer. “Every single working person out there can tell you, whether they have a great union-negotiated plan or they have very poor health insurance to no health insurance, that this health care system is completely broken and not working for us.”

New Hampshire resident Maryalice Cookinham said she supported Sanders “because he wants Medicare for All” and “that’s my No. 1 issue” — "I know friends who can’t get cancer treatments because they don’t have enough insurance.”

His intense focus on health care was enabled by the fact that his moderate rivals had spent the last week brawling — a stroke of luck that would end if centrists consolidated behind a candidate.

Even so, Sanders faced a significant challenge in the days before the primary. After Pete Buttigieg’s strong performance in Iowa’s caucuses, the former South Bend, Ind. mayor surged in the polls in New Hampshire. Sanders’ team kept a close watch on his rise, and Sanders criticized Buttigieg on the debate stage and trail for having billionaire donors. His campaign even released a negative online video about Buttigieg’s fundraising, a rare move for Sanders.

At the same time, Joe Biden bashed Buttigieg’s lack of experience in a digital spot, while Tom Steyer did the same in TV advertising. Amy Klobuchar also clobbered Buttigieg in the debate. That was enough to throw enough sand in Buttigieg’s gears and keep him from completely taking off in New Hampshire. But with 94 percent of precincts reporting, Buttigieg still finished less than 4,000 votes behind Sanders. Klobuchar placed third.

“It’s clear he would have lost if the moderate vote had coalesced around one candidate,” said Matt Bennett, co-founder of the moderate think tank Third Way, of Sanders.

Democracy for America, a progressive organization, released a statement Tuesday from chairman Charles Chamberlain that acknowledged that Sanders benefitted from the centrist-on-centrist attacks and stressed the need for left-wing unity.

“Progressives should have no illusions about what tonight’s victory means,” he said. “While the slow-motion implosion of the Biden campaign and the circular firing squad on the party’s right has thrown the Wall Street wing into disarray, we fully expect them to try to marginalize this win, pit progressives against each other, and spend millions to stop the growing grassroots movement for progressive change.”

The fact that Elizabeth Warren finished in fourth place and with no delegates in New Hampshire is good news for Sanders: It means he theoretically should have an easier time consolidating the progressive vote. But that won’t happen automatically, and Warren has signaled that she is in the race for the long haul.

But the attrition from Warren has already started. Part of the reason Sanders was successful Tuesday was because he won over very liberal and young voters by double digits, and Warren did not. When Warren was at the top of the polls last year, she siphoned off progressive and young voters from Sanders.

A Sanders adviser said that his polling went up sharply in New Hampshire around the same time he began airing ads on television. With less competition on air than Iowa, the person said, “we were able to communicate to voters more directly” and “re-established our base.”

Sanders’ success Tuesday is major vindication for a campaign that had been dismissed for months by political insiders and media. It also represents a turnaround from the dissension and staff upheaval in New Hampshire last year: In September, Sanders reassigned his then-state director and parted ways with his longtime senior adviser in New Hampshire. His steering committee fretted at the time about losing, and some members even eyed Warren.

Rep. Ro Khanna, Sanders’ campaign co-chair, said Tuesday that he gives the “most credit” to New Hampshire state director Shannon Jackson, “one of Sanders’ most loyal aides” who worked to “make sure the organization was fulfilling Sanders’ mission” after he took over the state operation amid the discord.

Sunrise Movement, a group of young climate change activists, also played a key role by campaigning for Sanders in New Hampshire. They reported making 33,000 calls to the state’s voters in the last week alone and collecting 12,000 pledge-to-vote cards from young people with the help of the New Hampshire Youth Movement. Sanders was also aided by a grassroots army of volunteers: According to his campaign, they knocked on 850,000 doors in New Hampshire since he jumped into the race.

“From Iowa to New Hampshire, we are showing people all across the country that organizing around the climate crisis and the Green New Deal is a decisive way to win an election,” said Sunrise Movement co-founder Varshini Prakash. “The climate crisis, along with health care, education and inequality, are defining issues for our generation. If we keep this momentum up and sustain historic levels of youth turnout, we will be the generation that steered the Democratic Party away from systemic breakdown and toward a prosperous, safe future.”

As the primary moves to more diverse states, Sanders showed other strengths that could come into play: He won over Latino voters in New Hampshire as well as at high-density Latino caucus sites in Iowa, per exit polling and an independent analysis. And along with being the favorite of voters under 45, Sanders also performed best with people without a college degree and those whose household income is less than $50,000 a year — data that his team is pointing to in order to make the case that he is the strongest candidate to take on President Donald Trump.

“We won because Bernie put together the multi-racial, working-class coalition that is going to win the nomination and the general election,” said Jeff Weaver, Sanders’ senior adviser.