Bernie Sanders has re-entered the 2016 presidential campaign in a big way as the Democratic party machine pulls out all its electoral weapons to stem a late surge in support for Donald Trump.

While most polls suggest that Mrs Clinton is leading Mr Trump in the national popular vote, her election advisers are worried that she may still not win next Tuesday’s election because of an expected low turnout of African-Americans and young voters in a raft of swing states.

In the 2000 presidential race Democratic nominee Al Gore lost to George W. Bush even though he won more votes.

Mr Gore lost because his support was concentrated in Democrat strongholds such as New York and California, while Mr Bush’s vote was more evenly spread across battleground states.

America’s leading election forecaster Nate Silver warned on Friday that Mrs Clinton could face a similar predicament this year because there were signs that her electoral support was starting to erode in swing states such as Nevada and New Hampshire.

Moreover, her national vote is holding up only because she is increasing her support in many southern states where Mr Trump still holds commanding leads.

The warning comes after the Clinton campaign was rocked once more by an information dump from Julian Assange’s WikiLeaks organisation, which has consistently released private correspondence that could discredit the Democrat candidate and her backers.

Mr Silver, who is widely respected for his innovative use of statistical research methods to predict election outcomes, says Mrs Clinton is in a much weaker position than President Barak Obama was in the final week of the 2012 campaign.

“She’s polling a little better than Obama was in the highly-educated swing states of Virginia, North Carolina and Colorado,” Mr Silver wrote on his Fivethirtyeight blog.

“But it’s only a little bit better — not a lot better — because African-American turnout for Clinton may be lower than it was for Obama in North Carolina and Virginia, and because third-party candidates may be eating into her margin in Colorado.”

Clinton and Sanders appear on stage together at a rally in North Carolina during the week.

Vermont senator Bernie Sanders, who challenged Mrs Clinton for the Democratic nomination earlier this year, will be a fixture alongside her at public rallies for the rest of the campaign.

Party strategists are hoping he can help stem a slide in support for Mrs Clinton among young voters, who are indicating to pollsters they will not vote at the November 8 election.

Mr Sanders appeared at a Clinton rally in New Hampshire on Wednesday and followed up the next day with a fiery speech in front of 6000 university students in North Carolina.

Pharrell Williams joins Hillary Clinton and Bernie Sanders to make the case for a Clinton/Kaine Administration!

Watch & Please RT pic.twitter.com/Ug1UsV2lh1

— ҞALANI #Resist (@DontBooo_Vote) November 4, 2016

Also appearing beside Mrs Clinton in North Carolina was the best-selling African-American singer, Pharrell Williams.

At the weekend Mr Sanders will trumpet Clinton’s cause to political gatherings in other cliff-hanger states, including Iowa and Ohio.

Donald J. Trump: The worst candidate for president in the modern history of the United States. pic.twitter.com/nJJdY8jE4P

— Bernie Sanders (@BernieSanders) November 2, 2016

The differences between Hillary Clinton and Donald Trump are day and night. The stakes are too high to sit this out. https://t.co/8ttsSwcsnl

— Bernie Sanders (@BernieSanders) November 1, 2016

Not only is Donald Trump going to lose on November 8th, but next year he's going to start paying his fair share of taxes.

— Bernie Sanders (@BernieSanders) November 2, 2016

Trump trots out Melania again

In a week where the vitriolic messaging of the presidential rivals sunk to new lows via negative TV ads aired across the country, Mr Trump on Thursday leaned on his wife – Melania – to highlight his sensitive nature.

“Every time my husband learned of a factory closing in Ohio or North Carolina or Pennsylvania, I could see him get very upset,” she told an audience in Philadelphia.

Mrs Trump, a former fashion model, then went on to pan the rise of social media, saying it was “too mean and too rough” and prone to insulting children about their “looks and intelligence”.

Mrs Trump promised that if she became First Lady of the United States she would campaign to wipe out cyber-bullying.

Melania Trump hits the stage in Pennsylvania to talk her husband’s Presidential credentials.

Her comments were widely panned by political commentators who pointed out that she did not make any effort to address her husband’s controversial use of Twitter.

Mr Trump has used social media to attack the appearance of models and actresses, and last year mocked the appearance of fellow Republican candidate, Carly Fiorina.

“Look at that face,” he told Rolling Stone in September last year.

“Would anyone vote for that?

“Can you imagine that, the face of our next president?”