It's official. Joe Biden's campaign to face Donald Trump at November's election is in serious strife.

There is no shame in not winning the New Hampshire primary.

Bernie Sanders beat Hillary Clinton here by more than 22 per cent in 2016 and she recovered.

But for Mr Biden to finish fifth with no delegates and just 8.4 per cent of the vote is a devastating outcome for the former vice-president. It jeopardises his fundraising efforts, is likely to cost him endorsements and calls into question the viability of his candidacy.

Combined with his fourth-place finish in Iowa last week, the result undermines his main pitch to voters: that he is best placed to beat the current polarising President.

To be considered 'electable' you have to win elections

Joe Biden's campaign has tried to spin his results so far as "just the start of a marathon". ( Reuters: Ivan Alvarado )

Almost from the moment he entered the race last April, Mr Biden had appeared to be the moderate candidate of choice for middle-of-the-road Democrats.

He was never more than a weak frontrunner in a crowded field, but thanks to his widespread name recognition, opinion poll after opinion poll suggested he had a handy head start.

So worried was Mr Trump about the threat, the Commander-in-Chief ultimately became just the third ever president impeached after being accused of ordering Ukraine to dig up dirt on his rival.

But Mr Biden's campaign primary night "party" in New Hampshire was a pretty graphic representation of how far and fast he's plunged.

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Clearly booked at a time when expectations were much higher, there was plenty of parking outside the venue and plenty of space inside.

That's because few bothered to show up. For most of the night, members of the media outnumbered campaign staff and supporters.

Even the man himself skipped it, jetting off early, eager to get out of the state before the results rolled in.

His campaign tried to spin the result as "just the start of a marathon".

This is technically true. A candidate needs 1,991 delegates to win the Democratic nomination — Pete Buttigieg currently only has 22 and Bernie Sanders 21. The most decisive days of this long race are still to come.

Mr Biden has now retreated to South Carolina, a diverse state long-considered a "firewall" for him.

His partnership with Barack Obama has helped him gain strong support among the African-American community and his campaign is now betting the house on a big victory there.

But that fourth stop in the primary calendar is still 17 days away. Between now and then, he will have to perform credibly in Nevada and endure many negative news cycles.

Momentum is important, blood is in the water and although he's not definitely done, others now sense a real opening.

Other moderates are circling, sensing a chance

Pete Buttigieg's momentum continues, with the South Bend Mayor coming second to Bernie Sanders in New Hampshire. ( Reuters: Jim Bourg )

Two substantially younger Democrats made their case for snatching the moderate mantle in New Hampshire's primary.

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Mr Buttigieg, a mid-west small-town mayor finished second with 24.4 per cent of the vote and Minnesota Senator Amy Klobuchar came in third with 19.8 per cent.

But neither candidate is well known nationally and neither has demonstrated an ability to win races in less-white, more diverse states, so there are still serious question marks over how they will perform in the longer term.

Then there's Michael Bloomberg.

The billionaire will only jump into the race on Super Tuesday in early March, when the greatest number of states cast their ballots.

Amy Klobuchar cut into Joe Biden's moderate voter base in New Hampshire. ( Reuters: Gretchen Ertl )

On that one day, 1,357 of the 3,979 pledged delegates will be up for grabs.

Mr Bloomberg, a former New York mayor, has spent in excess of $US300 million of his own money on advertisements, bombarding the country's big population centres.

The success of this risky strategy has always seemed predicated on a big Biden stumble.

But a national poll this week suggests the plan could be paying off.

The survey from Quinnipiac University had Mr Bloomberg surging into third on 15 per cent, behind Mr Biden on 17 per cent and Senator Sanders on 25 per cent.

Sanders strengthens hold on party's progressive wing

Bernie Sanders claimed victory in the New Hampshire primary with his wife by his side. ( Reuters: Rick Wilking )

The deep split among moderate and conservative Democrats is somewhat obscuring the much clearer picture on the left-wing of the party.

Senator Sanders has emerged from Iowa and New Hampshire in a formidable position, as he tries to build a progressive version of the wave that swept Mr Trump to power.

His campaign continues to complain it's not getting enough credit or media coverage.

Supporters said they were unfairly written off four months ago when the 79-year-old had a heart attack. They insist he will continue to defy expectations.

Senator Sanders now has more cash than any of his contenders who aren't billionaires, he has a core of passionate, loyal followers and seems to be smothering the chances of fellow left-wing senator Elizabeth Warren.

After finishing with just 9.3 per cent of the vote in New Hampshire, she is also in serious trouble.

Sanders in the box seat but still faces hurdles

Bernie Sanders says he can win the general election with a coalition of young and first-time voters. ( Reuters: Mike Segar )

However, there are still some big hurdles for Senator Sanders to overcome.

His 25.8 per cent share of the New Hampshire vote is a historically low amount for a winner to receive.

He's certainly not running away with the race yet, though he might have booked his spot in the final two.

Senator Sanders will also have to contend with increasingly pointed criticism from within his own party and probably the President.

Many Democrats are worried he doesn't have what it takes to win a general election and are hoping the 75 per cent of voters not supporting him right now will coalesce around another candidate.

But with Mr Biden nosediving, the party's establishment is now seriously reckoning with a prospect it has dismissed for months:

Senator Sanders has cemented his status as the frontrunner. If anxious moderates remain too divided for too long, they could struggle to stop him.