The Democratic Party’s seven strongest presidential contenders are preparing for what could be the fiercest debate stage clash of the 2020 US primary season as candidates look to survive the gauntlet of contests that lie ahead.

The field has been shaken and reshaped by chaotic Iowa caucuses earlier this week, and Friday’s debate in New Hampshire – coming four days before the state’s primary – offers new opportunity and risk for the shrinking pool of White House hopefuls.

Two candidates, Vermont Senator Bernie Sanders and former Midwestern mayor Pete Buttigieg, enter the night as the top targets, having emerged from Iowa essentially tied for the lead.

Those trailing after the first contest – including former vice president Joe Biden, Massachusetts Senator Elizabeth Warren and Minnesota Senator Amy Klobuchar – have an urgent need to demonstrate strength.

US presidential election 2020 key dates
(PA Graphics)

Billionaire activist Tom Steyer and New York entrepreneur Andrew Yang are fighting to prove they belong in the conversation.

The rapidly evolving dynamic means that the candidates have a very real incentive to mix it up with their Democratic rivals in the debate hosted by ABC, as they may not get another chance.

“This is the time when voters are eager for candidates to show they can compare and contrast, but also show they’re in it to win it,” said Democratic strategist Lily Adams, who worked on California Senator Kamala Harris’s unsuccessful 2020 presidential campaign.

“Expect it to get more feisty.”

The stakes are particularly high this week for Mr Biden, who has played front-runner in virtually every one of the previous seven debates, but left Iowa in a distant fourth place.

While reporting irregularities have blunted the impact of the Iowa contest, Mr Biden’s weakness rattled supporters, who encouraged him to take an aggressive tack on Friday night.

One of Mr Biden’s more prominent New Hampshire backers, Democratic operative Jim Demers, said this is the time to fight.

Democratic presidential candidate Joe Biden
Democratic presidential candidate Joe Biden (Mary Altaffer/AP)

“People want to see the fire, they want to see fight and they want to see the differences,” he said.

Mr Biden has adopted a decidedly more aggressive tone with his rivals in the days leading up to Friday’s debate, having largely avoided direct attacks against other Democrats for much of the last year.

The former vice president went after Mr Sanders and Mr Buttigieg by name and questioned their ability to beat Mr Trump.

On Mr Sanders, Mr Biden seized on the senator’s status as a self-described democratic socialist.

And on Mr Buttigieg, he knocked the 38-year-old former mayor’s inexperience.

Mr Biden also conceded the obvious – that his Iowa finish was underwhelming at best.

He called it a “gut punch” before embracing the underdog role, saying: “This isn’t the first time in my life I’ve been knocked down.”

The debate is the first since a progressive feud erupted on national television between Mr Sanders and Ms Warren.

The Massachusetts senator refused to shake her New England neighbour’s hand and accused him of calling her a liar moments after the January 14 meeting in Iowa.

Elizabeth Warren and Bernie Sanders after a Democratic presidential primary debate
Elizabeth Warren and Bernie Sanders after a Democratic presidential primary debate (Patrick Semansky/AP)

The pointed exchange threatened to cause a permanent fissure in the Democratic Party’s far-left flank.

Ms Warren has embraced her gender as a political strength in the weeks since, highlighting the successes of female candidates in the Trump era and her own record of defeating a male Republican to earn a seat in the Senate.

Mr Buttigieg should expect to be under attack on Friday night, said Joel Benenson, a debate adviser to Mr Buttigieg last year and a prominent Democratic pollster.

“He’s got to be prepared for incoming from the people behind him, who are going to be punching up and trying to take votes away,” Mr Benenson said.

“He’s got to be prepared to counterpunch, as well, and push back strenuously, but drive his message even when he’s responding,” he added.

“If they draw sharp contrasts, he has to as well.”