Mayor Martin J. Walsh is firing up his political machine and unleashing volunteers to rally for Democratic nominee Hillary Clinton in New Hampshire and beyond.

Walsh, serving as a surrogate, told volunteers at a Wednesday evening rally at Faneuil Hall that too much is at stake in the general election to allow Donald Trump, the Republican presidential nominee, to win the presidency. Likening the race to the hard-fought presidential primary, Walsh stressed the urgency of the Nov. 8 election.

“We have a huge opportunity to make a big impact up in New Hampshire,’’ Walsh told the cheering crowd, promising to send teams to the swing state every weekend until Election Day. “But I’m going to need you. We are going to need to make an impact. We’re going to [expect] you to take a trip to New Hampshire every weekend.’’

Since Clinton announced her presidential bid last year, Walsh has been an ardent supporter. He spoke on her behalf at the Democratic National Convention this summer. He endorsed her in the Democratic primary over a populist challenger, Senator Bernie Sanders of Vermont, and he sent more than 1,000 volunteers to New Hampshire in February to stump for Clinton.

Clinton lost the New Hampshire primary, and this week polls show her lead over Trump shrinking to single digits. But her campaign is counting on a solid, well-organized ground game to persuade skeptical voters in the key battleground state.

“Donald Trump does not have this,’’ said Nick Black, the Massachusetts director for the Clinton campaign, at the rally. “We have the ground game that is going to turn out voters for Hillary Clinton.’’

Trump campaign officials shrugged off the Walsh effect, saying it “will have no impact on our game whatsoever’’ and that real estate billionaire has “volunteers knocking on doors seven days a week, across the state.’’

“Is our campaign worried? Absolutely not. Hillary Clinton needs out of state volunteers, due to the enthusiasm being so low amongst her New Hampshire supporters,’’ wrote the Trump campaign in an e-mail response to the Globe.

Walsh’s role in the national campaign follows a tradition of Boston mayors who have used their political operations to rally the forces across the state line. During his administration, former mayor Thomas M. Menino would send legions of his supporters to Manchester — Boston’s adopted city for Democrats — in key presidential races for Al Gore, John Kerry, and Barack Obama when they sought the nation’s top job.

In the Clinton-Trump sprint to Nov. 8, Walsh is pulling from the army of volunteers who propelled him into office in 2013.

More than a thousand volunteers are expected to flood Manchester by Election Day, to knock on doors, mobilize voters, and try to persuade residents still on the fence about Clinton, said Megan Costello, a volunteer with the Clinton campaign who also works in the Walsh administration.

Walsh signaled at the rally that he was willing to go where the campaign takes him — to New Hampshire or Pennsylvania.

“We know that we have strong support in Massachusetts here,’’ said Costello, who was Walsh’s mayoral campaign manager. “But we also know that there are surrounding states like New Hampshire, for example, that have the polls very close.’’

Costello, currently the executive director for the Mayor’s Office of Women’s Advancement, spoke to the Globe on her lunch break.

Trump’s campaign said its door-knocking is 50 percent ahead of where the Republican Party was in 2012. And on Friday it will begin its National Week of Action, with 90 locations throughout the state where volunteers will meet and go door to door.

“With less than 50 days to go, Hillary Clinton’s campaign is relying on liberal Mayor Marty Walsh to parachute in volunteers to prop up her lagging campaign,’’ said Johanna Persing, a spokeswoman for the Republican National Committee. “New Hampshire voters already soundly rejected Clinton’s campaign and no amount of out-of-state door knockers will be able to build enthusiasm for their dishonest candidate.’’

Walsh had traveled to Concord on Saturday to deliver the keynote address at the Merrimack County Democrats’ annual supper. The event was held at the Carter Hill Orchard and featured New Hampshire Governor Maggie Hassan, a Democrat locked in a tight contest with Senator Kelly Ayotte, a Republican, for Ayotte’s seat.

Meghan E. Irons can be reached at meghan.irons@globe.com. Follow her on Twitter @meghanirons.