Michelle Obama campaigns with her 'girl' Hillary Clinton

At a rally in the swing state of North Carolina, the former rivals heaped praise on each other's commitment to public service, women and children.

Mrs Obama said Mrs Clinton was the most prepared candidate for the presidency ever, including both their husbands.

The display of unity follows past friction between the two of them.

But on Thursday the two sought to convince the crowd their relationship was more than a political alliance born out of shared interests.

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Mrs Obama has been recruited to secure her husband's legacy by helping to elect another Democratic president.

Flotus mastery rubs off, says BBC's Kim Ghattas, in Winston-Salem

Michelle Obama said it herself: it is unprecedented for a sitting first lady to be on the campaign trail in such a way, even more so to be campaigning for a former first lady who was once in the rival camp.

But the tensions of 2008 have long evaporated. Mrs Obama had taken an indirect swipe at Mrs Clinton then, telling voters that "if you can't run your own house, you certainly can't run the White House".

But there is a new history since, one where Mrs Clinton served President Obama loyally and where she would become the guardian of his legacy if she wins.

The women's first joint appearance on the trail was a warm, genuine affair. Mrs Obama came on stage sounding emotional after the tribute that Mrs Clinton had just paid her.

She described the presidential candidate as a friend. The crowds were more excited than any I've seen previously on the trail, drawn by the hugely popular Mrs Obama.

She is not only a powerful surrogate but an effective orator who speaks from the heart. Some of her mastery rubbed off on Mrs Clinton, who by her own admission is not a gifted speaker on stage, but was at her warmest ever sharing the stage with Flotus.

Mrs Clinton, meanwhile, is hoping that some of the first lady's popularity rubs off on her.

The event at Wake Forest University in Winston-Salem drew some 11,000 people, one of largest crowds of Mrs Clinton's campaign.

The former secretary of state spoke first to promise that as president she would continue with the "legacy that President Obama has built".

She praised the first lady, saying: "Seriously, is there anyone more inspiring than Michelle Obama?"

Then Mrs Obama took to the stage, saying of the former first lady: "Yes, she is absolutely ready to be commander-in-chief on day one.

"And yes, she happens to be a woman!"

She said Mr Trump's strategy was to "make this election so dirty and ugly that we want no part of it".

"They are trying to take away your hope," she told the crowd.

Mrs Obama also called Mrs Clinton "my friend" and described their shared experience of raising children in the White House.

The two were promoting Mrs Clinton's plan to deliver $500m (£411m) in funding to states that develop anti-bullying initiatives.

But the Clinton campaign hopes Mrs Obama's imprimatur will help galvanise female voters, especially black women.

There was tension between the two of them during the 2008 presidential campaign when Mrs Obama questioned Mrs Clinton's "character".

The women, both Ivy League-trained lawyers, are known for their contrasting styles as first ladies.

Like many of her predecessors, Mrs Obama has hewed closely to non-partisan issues, focusing on healthy eating and support for military families.

While she was first lady, Mrs Clinton had an office in the West Wing and made a doomed attempt to overhaul US healthcare.

While Mrs Clinton harboured political ambitions beyond her husband's presidency, Mrs Obama does not seem interested in pursuing her own political career further.

Early voting has been under way for the past week in North Carolina, with about one million ballots cast, around the same as in the last presidential election.

President Obama won the east coast state in 2008 with less than 15,000 votes, but lost there in 2012.

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What happens next?

• The two candidates will spend the remaining 12 days before the election criss-crossing the country in their bid to persuade undecided voters. Expect to see lots of appearances in battleground states such as Ohio, North Carolina, Florida and Pennsylvania
• Voters will go to the polls on Tuesday 8 November to decide who becomes the 45th president of the US
• The new president will be inaugurated on 20 January 2017

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