Sen. Bernie Sanders signs autographs during a town hall meeting in Conway, N.H. (Cj Gunther/European Pressphoto Agency)

Upstart presidential candidate Bernie Sanders is about to make a direct pitch to the Democratic Party establishment: Consider me, not Hillary Clinton.

Sanders huddled with advisers at his home here Wednesday to chart what he describes as the second phase of a campaign that has exceeded all expectations but still lacks the infrastructure and support from the party elites that could help him compete with Clinton on a national level.

He said he will issue a slew of detailed policy proposals, including for a tax system under which corporations and the wealthy would pay significantly more for initiatives that would benefit the poor and middle class, and will pour resources into voter outreach in early nominating states.

The senator also will appear with other White House hopefuls this week at a meeting of the Democratic National Committee and will urge party leaders to embrace him as a candidate who can attract new voters and energy, just as President Obama did eight years ago.

“Smart members of the establishment will perceive where the excitement is, where the energy is, where the enthusiasm is, where the potential voter turnout is,” Sanders said in an interview.

The efforts come at a key juncture in the battle for the Democratic nomination. Sanders appears to hold a slight lead over Clinton in the latest polls out of New Hampshire, the early nominating state that eight years ago helped Clinton rebound — temporarily — after a disappointing finish in the Iowa caucuses.

Clinton’s standing, which has been diminished in part by continued questions about her e-mail practices as secretary of state, has also created a potential opening for Vice President Biden, who according to advisers is weighing whether to jump into the race.

Sanders, a self-described democratic socialist, said he recognizes the challenges ahead for him — including broadening his support among African American voters, who will be crucial in states such as South Carolina. But he argued that he has made a political career of defying expectations and shouldn’t be underestimated in an election where many voters are demanding something different.

“The pundits cannot believe — it’s beyond their worldview to believe — that somebody who is not part of the establishment, somebody who does not have a super PAC, somebody who does not have connections with George Soros and all the other billionaires, can actually win,” Sanders said. “But use your own eyes and see what you can see.”

Sanders said the first phase of his campaign was largely focused on introducing himself to a Democratic electorate that was far more familiar with Clinton. On Friday, he will address the DNC in Minneapolis.

While Sanders said he knows he will never be the favorite of the establishment, he said he believes he has the potential to change some minds. “I think some of these guys are maybe rethinking their initial commitments,” he said. “And some of them who are not committed — and there are many of them — may come over to us.”

Roughly one-fifth of the delegates who will pick the nominee at the Democratic convention are superdelegates — elected officials and other party leaders who are not bound by voting in their states. So far, those superdelegates have sided overwhelmingly with Clinton.

Longtime Democratic strategist Tad Devine, who was among the participants in Wednesday’s meeting here, said Sanders has the potential to assemble “not necessarily the same coalition, but the same kind of coalition” as Obama did in 2008. Sanders’s huge campaign rallies have been heavily attended by younger voters, and during his long political career in Vermont, he has demonstrated an appeal to lower-income voters from both parties.

The rallies have generated headlines and proven fertile ground for small-dollar fundraising that is sustaining the campaign. On Tuesday, volunteers at Sanders’s campaign headquarters, in a third-floor office suite off a downtown pedestrian mall here, were dutifully entering contact information from sign-in sheets into a database.

Campaign manager Jeff Weaver said the senator will continue to hold rallies but “phase two will be a more focused effort to reach out to undecided voters” in early nominating states. The campaign is spending heavily in Iowa, New Hampshire, Nevada and South Carolina — all of which have contests in February — and starting to evaluate strategies for a dozen states that have primaries or caucuses on March 1.

To date, Sanders has deployed 41 staffers to Iowa, 23 to New Hampshire and nine to South Carolina, aides said.

Another focus of “phase two,” according to Sanders and his aides, will be a series of detailed position papers and policy speeches that go well beyond his hour-long stump speech.

Sanders said he plans a major address on Wall Street reforms and to add more specifics to many of his ideas, including revamping the tax system. He has pledged to reverse the growing income inequality in the country and has laid out a set of costly priorities — including free tuition at public colleges and universities, a massive infrastructure program and a large youth jobs program — much of which would be paid for by taxing businesses and the wealthy.

“It’s easy to say we’re going to make the corporations and wealthy pay their fair share,” Sanders said. “What does that mean, exactly?”

He plans, too, to speak out more about foreign policy, a subject that gets relatively little attention in his stump speech.

Aides acknowledge that Sanders could open himself up to criticism by detailing plans that are considered outside the political mainstream. But the candidate said he owes it to voters to lay out what he would do as president: “These are terribly serious times, and the American people deserve to be treated as intelligent people.”

Dante Scala, a political science professor at the University of New Hampshire, said it will be instructive to watch how voters respond to Sanders’s tax proposal, particularly in the first primary state.

“There are a fair number of well-educated, fairly prosperous Democrats here,” Scala said. “It will be interesting to see, when he gets down to tax brackets, which voters he’s impacting.”

Sanders started the race better known in New Hampshire, which is next to Vermont, than in any other early nominating state. A recent poll showed him ahead of Clinton, 44 percent to 37 percent. In Iowa, Sanders’s numbers have also risen, but Clinton still maintains a lead of roughly 27 percentage points, according to an average of recent polls by Real Clear Politics.

While Vermont is 95 percent white and Sanders has little experience reaching out to minority voters, he recently made a high-profile hire of a national press secretary, who is African American, and he is taking other steps to build support in minority communities.

Sanders’s appeal in New Hampshire was evident during a swing earlier this week across the less-populated northern part of the state. He drew hundreds of people in a series of small towns, including Bob Usherson, a retired city planner who said he considers himself “a centrist” politically.

Sanders “makes as much sense as anyone I’ve been listening to lately,” said Usherson, 66, after an event in Berlin, N.H. “The main things that have been irking me the last several years, he’s hitting on.” Asked for examples, Usherson cited the financial meltdown that led to the recession and the war in Iraq.

In Conway, N.H., Frank Jost, a manager of a nonprofit organization, was among those who came to check out Sanders but said they had previously been leaning in another direction.

“I would probably be considered a supporter of Hillary, but Hillary has some issues right now,” said Jost, 55. He said he is intrigued by the groundswell of support for Sanders, but has reservations, too. “Most of his policies are a little to the left of my personal comfort zone.”