Biden has struggled to retain the frontrunner status that he claimed when he entered the crowded Democratic field in April.
He faces tough competition from progressive US senators Elizabeth Warren and Bernie Sanders, and from up-and-coming fellow centrist Pete Buttigieg, an Indiana mayor who is half Biden’s age.
The party elder statesman finds himself under relentless attack by Trump, who has branded him “corrupt,” without evidence, for his son’s dealings with a Ukraine energy firm.
Biden’s debate performances have been shaky, and questions have swirled about whether the candidate — who turns 77 on November 20 — has the stamina for a gruelling one-year campaign.
And Biden faced renewed scrutiny Friday after Mike Bloomberg, the billionaire ex-mayor of New York, suddenly signalled he could enter the race, possibly syphoning moderate voters away from the former vice president.
But Biden has shown resilience on the campaign trail and in national polls.
He appeared to shrug off the latest developments as he made his entrance to the New Hampshire secretary of state’s office, after celebrating with cheering and drum-beating supporters in the building’s crowded hallways.
“Alright, where do I sign, boss?” a confident Biden quipped as he took part in an early hallmark of US presidential races: filing at the 200-year-old statehouse in Concord to be on the ballot in the small New England state that votes second in the nominations process.
Biden has been here before; he ran for president in 1988 and again in 2008. But this year is his best shot at the presidency, despite his advanced age and intense competition.
After filing, Biden braved freezing temperatures and snow flurries to address a rally of about 100 supporters.
John Lynch, the popular former governor of the Granite State, described Biden as “genuine, caring and authentic, and I can’t wait for him to get into the White House.”
Biden is a party establishment favourite. But he pushed back at the suggestion he might be too cosy with the Democratic elite to inspire young voters and reach new voices.
“I am reaching them. I’m the only person in this race that has significant support” across the voter spectrum, Biden told reporters. “I’m ahead across the board.”
‘Unite the sides’
Biden leads in national polling. But he has slipped to fourth place in Iowa, which kicks off the nomination voting on February 3, and trails Warren in New Hampshire.
The state borders both Warren’s Massachusetts and Sanders’s Vermont, but Biden suggested he would give them no quarter.
“I’m not here to come in second,” stressed Biden, who attends a chilli cookout and a town hall in the state Saturday.
Voter Richard St. Pierre, 57, said he sees Biden as “the best opportunity” for Democrats to wrest the White House from Trump.
“He’s balanced, and he’s not going to come in and go right into sweeping change,” St. Pierre told AFP at the rally, referring to Biden’s moderate platform.
“Is he igniting all the youth, the college scene? Maybe not as much,” he conceded. “But you’re not going to appeal to everybody.”
A 19-year-old Harvard University student who identified herself as Saylor added that she has become a fan of Biden.
“I’m definitely looking for someone who is more moderate, who will unite the sides, who will be civil,” she said.
“I’m more concerned with policies that are realistic, than ones that are far-fetched.”
Biden has sharply criticized the universal health care plans put forward by rivals Warren and Sanders, known as Medicare for All, as being too costly.
Biden proposes expanding on existing Obamacare in a more gradual improvement of the system, while Buttigieg advocates a “Medicare for all who want it” approach, which would allow those happy with their private insurance to keep it.
Both men are currently in New Hampshire. Buttigieg on Friday launched a four-day bus tour of the state, including an energized town hall with 740 attendees in the southern city of Salem.
Nicole Fisher, 30, an executive assistant from nearby Manchester, said she was “100 percent” behind Buttigieg.
Biden, she said, symbolizes “old ideology, old rhetoric.”
“This is new, this is fresh, this is different,” she said of military veteran Buttigieg. “And it’s not just because of his political experience, it’s him at his core.”