Sanders' victory here caps a remarkable milestone for the self-described democratic socialist. Since announcing his unlikely campaign in April, the Vermont senator has developed a cult-like following of supporters and rallied the Democratic Party's progressive base, exposing serious vulnerabilities in Clinton's candidacy.
To a jubilant crowd gathered at a local high school gymnasium here, Sanders thanked his supporters for helping to send a message that he said would "echo from Wall Street to Washington, from Maine to California."
"And that is that the government of our great country belongs to all of the people, and not just a handful of wealthy campaign contributors and their super PACS," Sanders boomed.
He reminded the hundreds that were gathered here that his campaign had no organization and no money when it first launched nine months ago. But now, Sanders promised, the enthusiasm and energy behind his "political revolution" could take him all the way to the White House in November.
"Because of huge voter turnout -- and I say huge! -- we won," Sanders said, a reference to one of GOP front-runner Donald Trump's favorite catchphrases. "We harnessed the energy and the excitement that the Democratic Party will need to succeed in November."
The striking momentum behind Sanders' underdog campaign had also been on full display last week, when Clinton barely managed to eke out a win in Iowa. Clinton, whose 2008 defeat in that state to then-Sen. Barack Obama dealt a devastating blow to her first White House bid, celebrated the razor-thin margin victory.
But since Iowa eight days ago, Clinton has openly acknowledged that she has her work cut out for her -- particularly in boosting enthusiasm among younger voters.
It was a message she echoed in her concession speech on Tuesday night.
"I know I have some work to do, particularly with young people," she said. "Now we take this campaign to the entire country. We're going to fight for every vote in every state."
The polls heading into New Hampshire showed Sanders holding a consistent and sizable lead over Clinton. Even as Clinton campaigned throughout the state, her team was careful to downplay expectations heading into Tuesday.
In recent weeks, Clinton and her allies had signaled that they saw little hope of winning the Granite State. They had pointed out, for example, that Sanders had the advantage of hailing from the neighboring state of Vermont.
"We're doing everything we can to mobilize our supporters in these final hours," Clinton press secretary Brian Fallon told CNN's Wolf Blitzer Tuesday afternoon. "But there's no question that the favorite today is Sen. Sanders."
Sanders' victory Tuesday -- while widely expected -- is nevertheless consequential as the Democrats eye their next contest in Nevada on February 20.
Polling data from there has shown Clinton with a distinct lead in the state, where her campaign has been on the ground for many months.
But Sanders and his allies are committed to giving Clinton a tough race in Nevada. They've invested in their campaign infrastructure on the ground, and hope to use their strong finishing New Hampshire to boost their viability as they move on to Nevada, South Carolina and the March contests.
Moments after the state was called for Sanders, the senator's senior strategist, Tad Devine, told reporters at his victory party in Concord that they simply had a "better campaign."
"We are a better-organized campaign. We have more people on the ground. And as of today, I believe we have more resources, campaign to campaign, to expend," Devine said, when asked about the Clinton campaign's contention that she can put away the race in March.
The Clinton camp issued a memo Tuesday night that sought to highlight the campaign's long-game -- and dissuade supporters from focusing too much on the more immediate outcomes in New Hampshire, Nevada and South Carolina.
"The nomination will very likely be won in March, not February, and we believe that Hillary Clinton is well positioned to build a strong -- potentially insurmountable -- delegate lead next month," campaign manager Robby Mook wrote.
The political attacks between the two candidates have grown increasingly sharp and personal in recent weeks -- a trend that's likely to continue heading into Nevada. Sanders has overwhelmingly focused his attacks on the speaking fees the former secretary of state received from Goldman Sachs and her ties to Wall Street.
Clinton, meanwhile, has charged that Sanders is living in a fantasy and has unrealistic policy proposals, and Clinton allies have even accused Sanders backers of leveling "sexist" attacks against Clinton.