White House hopeful Pete Buttigieg fought off intensifying attacks from his Democratic rivals Saturday as they battled for votes in New Hampshire, stop two on the road to picking a challenger to President Donald Trump.

Buttigieg -- the former mayor of a Midwestern town of 100,000 -- has been widely branded by his opponents as too young and inexperienced to take on Trump, and after his Iowa finish the attacks have only sharpened.

Former vice president Joe Biden, fighting to keep his White House hopes alive after finishing an unnerving fourth in Iowa, tore into Buttigieg as they jostled for support from moderates.

Democratic presidential candidate Elizabeth Warren speaks at campaign event in Derry, New Hampshire Democratic presidential candidate Elizabeth Warren speaks at campaign event in Derry, New Hampshire Photo: GETTY IMAGES / JUSTIN SULLIVAN

Biden, 77, released a video contrasting the accomplishments of his decades-long political career against Buttigieg's as mayor of South Bend, Indiana.

The ad highlighted Biden's work on Obamacare and the Iran nuclear deal, while belittling Buttigieg's efforts to install decorative bridge lights and lay new sidewalks in South Bend.

Democratic presidential candidate Joe Biden finished a dismal fourth in Iowa Democratic presidential candidate Joe Biden finished a dismal fourth in Iowa Photo: GETTY IMAGES / SPENCER PLATT

Buttigieg's campaign responded that the ad "speaks more to where (Biden) currently stands in this race than it does about Pete's perspective as a mayor and veteran."

The former mayor, a political nobody at the national level a year ago but now a force to be reckoned with, seemed to revel in his new status.

Democratic presidential candidate Michael Bloomberg speaks at a campaign stop Detroit, Michigan Democratic presidential candidate Michael Bloomberg speaks at a campaign stop Detroit, Michigan Photo: AFP / JEFF KOWALSKY

Speaking to supporters in Keene on Saturday, Buttigieg said the election would define "what it's like to be an American for the next four years.

"I am the candidate that is prepared to defeat Donald Trump," he said.

In a state proud of its special place in American politics, even some of its houses have a historical connection to presidential candidates. Arnie Arnesen, bought the house of a former, powerful Democrat in 2009, but he wasn't it's only famous political c In a state proud of its special place in American politics, even some of its houses have a historical connection to presidential candidates. Arnie Arnesen, bought the house of a former, powerful Democrat in 2009, but he wasn't it's only famous political connection; Jimmy Carter, Bill Clinton, Al Gore and more recently Bernie Sanders have all stopped by during their campaigns. Photo: AFPTV / Eleonore SENS

On Sunday, Buttigieg was scheduled for what is known in Washington as the "full Ginsburg": appearances on the five major morning talk shows.

Democratic presidential candidate Bernie Sanders at a press conference at his New Hampshire campaign headquarters Democratic presidential candidate Bernie Sanders at a press conference at his New Hampshire campaign headquarters Photo: GETTY IMAGES / JUSTIN SULLIVAN

Later on Saturday at a dinner hosted by the state Democratic Party, Buttigieg appeared to take aim at Sanders, 78, a veteran senator calling for "political revolution," who has been challenged over his age and his "Medicare for All" health plan which has been labeled as too expensive.

"With a president this divisive, we cannot risk dividing Americans further, saying you must either be for a revolution or you must be for the status quo. Let's make room for everybody in this movement," Buttigieg told thousands of attendees in a university arena, some of whom replied with jeers.

Results of the US Democratic Party caucus in Iowa, with 100% of precincts reporting. Results of the US Democratic Party caucus in Iowa, with 100% of precincts reporting. Photo: AFP / Gal ROMA

Sanders used his appearance to tamp down tensions, acknowledging to the crowd "I know there are differences of opinion in the room. I feel that. I sense that."

"I know that whoever wins the nomination, we are going to come together to defeat the most dangerous president in this country's history," he said.

Senator Amy Klobuchar -- who assailed Buttigieg as a newcomer to national politics during a Friday debate -- kept up the attacks as she rallied supporters in New Hampshire.

Despite the Iowa setback, Biden sought to cast himself as best-placed to mount a centrist challenge to the Republican Trump, who this week survived an impeachment trial that did little to dent his electoral support.

"I've lost a lot in my lifetime, like a lot of you have," he told the dinner, referring to the deaths of his wife and daughter in a car accident and losing son Beau to cancer.

"But I'll be damned if I'm going to stand by and lose this election to this man," Biden declared.

Yet the former vice president has all but conceded defeat in New Hampshire, noting that in 2016 Sanders, who represents neighboring Vermont, won the New Hampshire primary by 20 points.

At a Biden rally Saturday, Erin Kerry, a 49-year-old financial analyst from neighboring Massachusetts, said she wished Biden had done better in the debate, but added, "I'm not ready to count him out yet."

Cameron Landry, a 24-year-old student, said he liked Biden's experience but questioned whether he had the grit to take on Trump.

"I think we need somebody that can compete with the reality star. People love reality TV. It's a dumpster fire and people want to watch," Landry told AFP.

After New Hampshire, the candidates turn to Nevada on February 22, South Carolina on February 29 and then Super Tuesday on March 3, when 14 states vote.

Also in the race is billionaire and former New York mayor Michael Bloomberg, who is surging in the polls after spending a record $260 million of his personal fortune on his campaign.