Donald Trump set for victory in New Hampshire primaries

As snowfall brought yet more uncertainty to the first-in-the-nation race's final hours, Mrs Clinton tried to move past talk of a shake-up in her campaign and controversy over comments by supporters that women should feel obliged to vote for her to become America's first woman president.

Campaigning across the north-eastern state with her husband, former US president Bill Clinton, and daughter Chelsea, she worked to flip Mr Sanders' favoured critique against her by claiming that he too had taken money from Wall Street - if only indirectly.

The New Hampshire primary traditionally plays a pivotal role by providing momentum to the winners heading into the next contests in South Carolina and Nevada.

Those candidates who fare poorly could see donations dry up and face pressure to withdraw from the race.

In the last 10 elections, the winner of the Republican primary went on to become the eventual nominee eight times; on the Democratic side, seven winners went on to become nominees.

Billionaire businessman Mr Trump launched the harshest attacks, not just against Texas senator Ted Cruz who had bested him in Iowa, but also against Jeb Bush.

The former Florida governor is one of three Republicans hoping that Florida senator Marco Rubio's recent stumbles have opened a fresh path for one of them to emerge as the more mainstream alternative to Mr Trump and Mr Cruz.

"Jeb is having some kind of a breakdown, I think," Mr Trump told CNN, calling Mr Bush, the son and brother of presidents, a spoiled child and an embarrassment to his family.

"I think it's a very sad situation that's taking place."

The enmity was mutual. Vying for votes in Nashua, Mr Bush described Mr Trump variably as a loser, a liar, a whiner and the worst choice for president.

He attacked what he said was Mr Trump's proclivity for "insulting women, castigating Hispanics, ridiculing the disabled and calling American PoWs losers".

Mr Trump also had a shot at Mr Cruz during a massive rally in Manchester last night.

When an audience member shouted out an insult directed at Mr Cruz - a vulgar term for "coward" - Mr Trump repeated the term and jokingly reprimanded the woman.

Cruz spokesman Rick Tyler responded via email, saying: "Let's not forget who whipped who in Iowa."

Still, Mr Trump was running ahead in pre-primary polls, as was Mr Sanders on the Democratic side as candidates race to collect delegates for the parties' national nominating conventions in July.

Not so long ago, Republicans saw New Hampshire as the proving ground that would thin out their unwieldy field of candidates.

Mr Rubio's surge into third place in Iowa a week ago raised the prospect that voters in New Hampshire would anoint him over Mr Bush, New Jersey governor Chris Christie and Ohio governor John Kasich.

Yet Mr Rubio faced fresh questions about his readiness and his ability to defeat the Democratic nominee after Saturday's debate, when he was mocked for reciting rote talking points about President Barack Obama over and over.

Growing doubts about Mr Rubio seemed to portend a fight for delegates to the party's national convention that could extend for weeks or months - to the dismay of Republican Party leaders hoping for a quick consolidation behind anyone but Mr Cruz or Mr Trump.

Democrats are already resigned to the likelihood of a protracted primary contest following Mr Sanders' strong performance in Iowa.

Sensing Mr Rubio's vulnerability, nearly everyone seemed to be on the attack.

Mr Bush's campaign debuted a new advert questioning Mr Kasich's conservative credentials, while an outside group backing Mr Rubio ran an ad assailing Mr Bush.

Mr Christie and Mr Bush both piled on Mr Rubio, claiming he had not been tested the way governors had.

In the week since Mrs Clinton eked out a win in the Iowa caucuses, her campaign has worked aggressively to lower expectations for New Hampshire, where Mr Sanders has maintained a sizeable lead despite Mrs Clinton's victory there eight years ago against then Illinois senator Barack Obama.

Mr Sanders, a Vermont senator, is well known to voters in neighbouring New Hampshire.

Wary of upsetting a race trending his way, Mr Sanders stuck to core campaign themes as he addressed cheering supporters in Nashua.

In recent days, Bill Clinton has accused some Sanders supporters of waging "sexist" attacks, and feminist Gloria Steinem and former secretary of state Madeleine Albright have criticised women who are not supporting Mrs Clinton.

Yet Mr Sanders passed up all thatyesterday, instead telling supporters in Nashua: "We have come a long way in the last nine months."

But his campaign did take issue with Mrs Clinton's claim that Mr Sanders benefited from Wall Street money donated to Senate Democrats' campaign arm, with campaign manager Jeff Weaver arguing it "suggests the kind of disarray that the Clinton campaign finds itself in today".