Following Bernie Sanders’s victory in New Hampshire, supporters are optimistic that the ‘Bern’ will gain momentum and spread to South Carolina and Nevada next. They also couldn't help but dance throughout the rally, going as far as dedicating some serious dance moves to the senator. (Alice Li/The Washington Post)

Sen. Bernie Sanders took a few moments in his victory speech Tuesday night to make a small request of his supporters: “Please help us raise the funds we need, whether it’s 10 bucks, 20 bucks or 50 bucks,” he said.

The response was so overwhelming that his website buckled under the traffic . Between the close of polls and 8 p.m. Wednesday, his campaign brought in $6.5 million, a single-day record for his campaign.

Sanders is barreling out of New Hampshire in a position that few expected when he entered the 2016 White House race: financially competitive with Hillary Clinton.

Boosted by an online fundraising juggernaut, the senator from Vermont has been scooping up donations at a faster clip than Clinton so far this year, giving him unexpected resources for the rush of coming votes in Nevada, South Carolina and the 11 “Super Tuesday” states that hold Democratic contests March 1.

Democratic presidential candidate Bernie Sanders thanked supporters for high voter turnout after winning the New Hampshire primary on Feb. 9. (Reuters)

Clinton started the year with $10 million more than him in the bank, but Sanders raised $20 million to her $15 million in January, helping him narrow her cash advantage. He had his previous best fundraising day to date in the 24 hours that followed his close loss in last week’s Iowa caucuses, collecting $3 million.

Sanders plowed some of his ballooning war chest into additional TV ads in New Hampshire, where he outspent Clinton on the airwaves in the final weeks before beating her resoundingly there. With more than 89 percent of precincts reporting, he held a lead of more than 20 percentage points.

His campaign plans to use its funding surge to build up its ground operations and roll out robust advertising campaigns in upcoming states.

“One of the big things that separates us from past insurgent campaigns is that we’ll have the resources to enable us to compete across a broad range of states,” said Tad Devine, a senior strategist for Sanders.

Devine said the campaign is planning to launch ads Wednesday in three Super Tuesday states: Colorado, Minnesota and Oklahoma. And he said it will expand its reach in a fourth: Massachusetts, where the campaign has been advertising in the Boston market to reach New Hampshire voters. Starting Wednesday, it will add markets in the southern and western parts of the state , Devine said.

Clinton — who outraised Sanders $114.4 million to $74.9 million in 2015 — has formidable financial resources, including a national network of donors that she and her husband, Bill Clinton, have cultivated over four decades. January marked her campaign’s best small-dollar and online fundraising month to date, and the pace has only increased in February, officials said.

“More than 700,000 people have contributed to this campaign, the vast majority giving less than $100,” the former secretary of state told supporters Tuesday night. “I know that doesn’t fit with the narrative. I know there are those who want to deny the passion and the purpose you all show every day for this campaign, but you are the reason that we are here, and you are the reason we are going to win the nomination, and then win this election together!”

Clinton’s operation has used its resources to make early investments that her team thinks will pay off. The campaign laid down the markers of a national-caliber organization early last year, when it temporarily dispatched staff to all 50 states to begin building local support for her. For months, Clinton has had paid organizers in states that hold primaries and caucuses in March, where they have been mobilizing volunteers and training precinct leaders.

Clinton is expected to be on friendlier terrain after New Hampshire, as the race moves to states with sizable populations of African American and Latino voters. In South Carolina in late January, she led Sanders by 37 percentage points in an NBC News-Wall Street Journal-Marist poll. African Americans and Latinos are also likely to account for a significant share of primary voters in delegate-heavy contests early next month in Texas, Virginia and Georgia.

Clinton has another potential advantage: millions of dollars that could be mustered by independent groups on her behalf. Priorities USA Action, one of the two pro-Clinton super PACs, was sitting on nearly $45 million at the end of last month.

“We’re going to do everything we can to make sure that Hillary Clinton is the next president, and we’re constantly assessing how best to do that,” said Guy Cecil, chief strategist for Priorities.

Still, Sanders’s ability to turn on an enormous cash spigot has provided his campaign with extra firepower as the race expands to a much larger playing field. He has deployed paid staff to all the states that vote through March 1, including 50 each to Nevada and South Carolina, where he is also running TV ads.

The senator used his win in New Hampshire to appeal for more money, telling a national television audience that instead of raising money from Wall Street, “I am going to hold a fundraiser right here, right now, across America.”

The resulting surge in online contributions broke the campaign’s traffic record and slowed its donation processing to a crawl.

Sanders’s fundraising success has prompted urgent email solicitations from Clinton’s campaign to her supporters.

“For the first time this campaign, we’re being outraised by our opponent,” read a Feb. 4 email from Clinton’s national finance ­director, Dennis Cheng. “This should be a very loud wake-up call.”

Sanders is drawing from an enormous base of more than 1.3 million contributors — nearly twice as many as Clinton has. The vast majority have contributed tiny sums online and can be repeatedly tapped for more money without reaching the maximum allowed under federal election rules.

Through the end of 2015, Sanders brought in nearly $47 million from donors who gave $200 or less — 64 percent of his total haul and more than twice as much as Clinton raised through contributions of $200 and under, according to an analysis by the nonpartisan Campaign Finance Institute.

It’s a fundraising operation that requires little traditional overhead. Unlike most candidates, Sanders does not have paid finance staffers assigned to cultivate fundraisers who bundle checks, and he has held just a handful of events to solicit larger donations.

Clinton leans much more heavily on wealthy backers: She raised 58 percent of her money in 2015 from contributors who gave the $2,700 maximum, according to the Campaign Finance Institute. She cannot turn to them again for support during the primary.

Sanders also has far lower operating expenses than Clinton, who has built up a massive operation. He spent $5.4 million on payroll in 2015 to her $25.4 million and $400,402 on travel to Clinton’s $1.8 million, campaign finance records show.

While Clinton has paid six polling firms more than $2.8 million combined, Sanders has only hired one pollster, Tulchin Research of San Francisco, which received $527,767 — all in the last three months of 2015.

He has plowed the majority of his money into TV and digital ads: $20 million by the end of 2015, according to Federal Election Commission reports. Clinton reported spending $18.3 million on ads.

Sanders is also being lifted by a network of advocacy groups. While he maintains that he does not have an allied super PAC flanking his campaign, a super PAC financed by National Nurses United has already spent more than $1.2 million on a bus tour, digital ads and billboards supporting him.

The nurses union is not letting up. It will deploy its signature red bus in Nevada and South Carolina in the coming weeks and roll out a “comprehensive” field program in Super Tuesday states, according to Michael Lighty, NNU’s policy director.

“We’re going to contest everywhere,” he said.

Clinton’s well-funded independent allies are also stepping up their engagement. So far, more than a dozen unions and women’s advocacy groups, such as Planned Parenthood, have reported spending more than $1.7 million to support her. The Service Employees International Union doled out more than $564,000 on voter outreach in South Carolina just this week.

Gold reported from Washington, Wagner from Concord, N.H. Scott Clement and Anu Narayanswamy in Washington contributed to this report.