"I'm not going to say I'm delighted," said Brynn McDonnell, 24, a former Sanders volunteer in the audience, when asked about the Clinton endorsement. "I think it's a political move he has to make."
"There are some Bernie supporters who want to go for Trump, and it's important for people to understand that Bernie is the antithesis of Trump," explained McDonnell, who recently moved to New Hampshire from Iowa.
The rally began with two Sanders supporters speaking: environmental leader Bill McKibben and Jim Dean, the leader of Democracy for America, a grassroots group that endorsed Sanders in the primaries.
Dean announced that his group would now be throwing its support behind Clinton.
McKibben touted Sanders's appeal to young voters and said he hoped the Democratic party would "not disappoint them" going forward.
"Secretary Clinton, we wish you Godspeed in the fight that now looms," McKibben said.
Underscoring the theme of unity, New Hampshire Governor Maggie Hassan and U.S. Senator Jeanne Shaheen -- both Clinton supporters also addressed the crowd before Clinton and Sanders appeared.
Although Clinton effectively clinched the nomination last month, aides said Sanders has no plans to suspend his campaign or formally exit the race before the convention two weeks from now in Philadelphia. In the past, they have suggested this could give Sanders more leverage in pushing for more changes in the party platform before it is adopted.
That approach was successful to a significant degree, though it alienated many Democrats who thought the senator should have been more gracious in accepting defeat after a grueling nominating process.
In the past week, Clinton has agreed to push policies on free college tuition and expanded access to health insurance that reflect positions Sanders championed during the primaries. And he has claimed some major wins in the party's platform, including support for a $15 federal minimum wage and measures to combat climate change.
The joint appearance here was greeted with a news release from the Trump campaign highlighting the "top five reasons Sanders supporters will never be excited about Hillary Clinton."
One of them was her past support for international trade deals, which Sanders repeated criticised during the primaries. Trump has tried to reach out fo Sanders supporters on that issue, particularly those in the Rust Belt, where thousands of manufacturing jobs have benn shed.
It remains to be seen how active Sanders will be on the campaign trail for Clinton -- and how much he can do on her behalf.
A Washington Post-ABC News poll released late last month showed that only 8 percent of Sanders supporters said they would back Trump over Clinton in the general election, down from 20 percent a month earlier. The greater fear for Democrats is that Sanders voters might simply stay home.
Aides to the two candidates have discussed sending Sanders to states where he performed well in the primaries, including Michigan and Wisconsin. New Hampshire also fits that category; Sanders defeated Clinton here by 22 percentage points in the February primary.
Clinton was scheduled to fly to New York after her rally with Sanders on Tuesday for a special peformance of the hit musical "Hamilton," which is also doubling as a fundraiser for her campaign.
Clinton also plans later this week with a potential running mate, Sen. Timothy M. Kaine, D-Va. The two are scheduled to appear together Thursday afternoon in Annandale. Virginia is among the eight battleground states that Clinton is targeting with television advertising.
