For Representative Dean Phillips, challenging President Biden in the Democratic primary race has produced some humbling moments, like when he failed to draw a single voter to a meet-and-greet this month.

“Sometimes if you build it, they don’t come,” he told reporters then.

But on Thursday, they did come to campaign events for Mr. Phillips, who had to squeeze through a crowd at the University of New Hampshire at Manchester.

Whether the gathering — a mixture of disillusioned Democrats, undecided voters and curiosity-seekers — was for him or the man standing to his right was another story.

He was flanked by Andrew Yang, whose unsuccessful run for president in 2020 brought him some star power as he developed a devoted internet following known as the “Yang Gang.”

Mr. Yang formally endorsed Mr. Phillips later on Thursday, five days before New Hampshire holds the nation’s first primaries. He argued that Mr. Biden would be a liability if he faced former President Donald J. Trump again in the November election.

“Joe Biden, who I supported the last time, in my view, is going to deliver us to Trump the sequel,” Mr. Yang, who left the Democratic Party in 2021, said in Manchester. “Dean Phillips saw this, and said: ‘You know what? I am going to do something about it.’”

Mr. Phillips, a House Democrat from Minnesota who formerly co-owned Talenti Gelato and introduced Belvedere Vodka to the United States, has poured millions of dollars from his personal fortune into his bid. Since entering the race in October, he has modulated his message between moderate and progressive positions, and he is trying to seize on Mr. Biden’s absence in New Hampshire.

Mr. Biden declined to have his name placed on the ballot in Tuesday’s primary after Democrats in the state refused to move their contest back to allow South Carolina, the state where Mr. Biden revived his 2020 candidacy, to vote first.

The president had lobbied the Democratic National Committee to change its calendar, rankling party members in New Hampshire and leaving his supporters to write in his name.

“It is repulsive,” Mr. Phillips said. “It is suppressive. I think it is downright unconstitutional and certainly anti-democratic.”

Mr. Phillips, who turns 55 on Saturday, has hammered away at Mr. Biden’s low approval ratings and age — the president turned 81 in November — during his campaign.

David Simon, 67, a retired lawyer from Santa Barbara, Calif., who traveled to New Hampshire to volunteer for Mr. Phillips and worked for his 2018 congressional campaign, said that he had no illusions.

“It’s just a moonshot, but somebody had to jump in and raise these issues,” he said before the event in Manchester, the first of two featuring Mr. Yang.

After Mr. Phillips’s second event on Thursday, in Hanover, N.H., Xavier Laack, 19, a Dartmouth College student from Rochester, Minn., said he hoped that Mr. Phillips could eke out a victory in the primary, though he acknowledged that the chances were slim. The event was the second Phillips campaign event Mr. Laack had attended, and he said the turnout was stronger.

“Last time was like, ‘I’ve got to be realistic, he’s not going to win,’ but this time it’s more promising,” he said. “He’s probably still not going to win, though.”

Mr. Laack persuaded three classmates to tag along, insisting they had to hear the congressman speak before Tuesday’s primary.

That wasn’t their only motivation. Martin Skacel, also a 19-year-old Dartmouth student, sat with Mr. Laack in the front row, and said before the event that Mr. Yang was the evening’s main draw for him.

“I’m excited to hear him,” Mr. Skacel said. “That’s what brought us out.”

Inside the cramped space in Manchester, news crews from Germany and C-SPAN chronicled the proceedings, which, in addition to focusing on Mr. Phillips’s unlikely challenge, included a discussion about artificial intelligence.

Ashleigh Rourke, 46, a mother of three and a Democrat from Exeter, N.H., said that she had tried to rally her neighbors to attend a recent event for Mr. Phillips at a bookstore, but that it was a struggle.

“It’s frustrating,” she said. “Our house is not even a half-mile from the bookstore.”

Paige Leary, 55, a mother of four and independent voter from Exeter, was wearing an “I’m Keen on Dean” button. She said that Mr. Biden was no lock to win re-election and that she was having flashbacks to 2016, when she voted for Hillary Clinton.

“She did expect a coronation, and boy, were we surprised, and not in a good way,” she said.

Mr. Phillips, a longtime moderate during his three terms in the House, raised some eyebrows when he embraced “Medicare for all,” the proposal for universal health care championed by Senator Bernie Sanders.

More recently, he drew scrutiny when a header on his campaign website for “Diversity, Equity, and Inclusion” vanished and was replaced with “Equity and Restorative Justice.” It came after a super PAC supporting him was expected to receive $1 million from William A. Ackman, the billionaire investor who in recent months has become an outspoken critic of D.E.I. programs in higher education.

At the Hanover event, Mr. Phillips called himself “incorruptible” and accused his colleagues in Congress of spending their time appeasing donors and “dialing for dollars.”

“It is the most sickening form of legalized corruption I can ever imagine possible,” he said.

After Mr. Phillips concluded his remarks in Hanover, students and supporters lined up for their chance to take a photograph with him. Speakers overhead played the comedian Bo Burnham’s song “Biden,” an electronic beat thumping under the catchy chorus: “How is the best-case scenario Joe Biden? / They’re really going to make me vote for Joe Biden?”

Mr. Phillips’s message resonated with Gabriele Currier, 68, a retiree from Enfield, N.H., who plans to vote for him.

“I am pretty energized by this man,” she said. “He’s got such great ideas. He’s articulate and I just love what he has to say. He’s the dude.”

After the first gathering, a white campaign van plastered with two Phillips yard signs was offered to whisk news media members from a campaign office to the second event, a practice that is common with many larger and well-financed campaigns.

Three people loaded in the vehicle across from Mr. Phillips’s headquarters in Manchester, where a handwritten note on the front door listed office hours and a contact number for the campaign. One was wearing a campaign button. A second was identified by the campaign as a correspondent for a newspaper in Spain.

Then there was Link Lauren, 25, who described himself in an interview on Friday as a Dallas-based TikTok journalist and New York University graduate. His TikTok page, which has over 400,000 followers, has videos of him interviewing Vivek Ramaswamy and Robert Kennedy Jr.

He said that he had reached out to the Phillips campaign to let it know he was in New Hampshire, and then came an invitation to ride in the media van.

“I think the reason they had the van was because of me,” he said. “I didn’t rent a car.”