Michelle Obama made clear this week that she is all-in for Hillary Clinton's presidential campaign.

Her captivating speech was an early turning point for Democrats after a rocky start to their convention - and made an emotional case for electing Clinton.

The question now is: How much will the first lady campaign for the newly minted Democratic nominee?

Both Obama and her husband are expected to campaign in earnest for Clinton in September and October.

The Clinton campaign sees the first lady as a unifying presence with the potential to heal some of the rifts within the Democratic party. Clinton campaign manager Robby Mook said he hopes she "will continue to do what she did in her speech, which is talk about the important role that the president plays as an advocate for kids and families, and how Hillary is eminently qualified to do that job probably better than anyone else in history".

In her convention address, the first lady managed to pointedly criticise Trump as a poor role model - but without ever mentioning his name. Clinton's campaign hopes to see more of the same.Other surrogates, including President Barack Obama and Vice-President Joe Biden, are expected to take on more of an attack-dog role, going directly after Donald Trump.

Obama also made the case for the Democratic nominee by speaking emotionally about the historical barrier that Clinton could break. It is possible that the two women will campaign together - even though Michelle Obama runs the risk of outshining Clinton if they share a stage.

Clinton has acknowledged that she is not a charismatic political figure. Still, her team likes the idea of her putting her growing chemistry with Obama on display, now that old tensions from the bitter 2008 primary race seem to have evaporated.

Tina Tchen, the first lady's chief of staff, described the connection between the fellow first ladies as "very warm" and said Obama "has tremendous respect for Secretary Clinton's lifetime of leadership and devoted service to our country".

But for all her political star power, Obama does not enjoy the grind of the campaign trail, and she tends to ask campaign strategists to pick and choose their efforts to deploy her.

Stephanie Cutter, a political consultant who was a top aide to the Barack Obama campaigns, said the first lady is a careful planner who will probably take control of her schedule. She campaigned "very hard" for her husband, and her pitch for Clinton "makes you think in both a broad yet personal way about the country and their family. It takes it outside of politics".

"In 2008, she was known as the closer for President Obama and she will play that role for Hillary this election, by talking about how America's children need Hillary to be their next president," said Kristina Schake, the Clinton campaign's deputy communications director, who previously served as Michelle Obama's White House communications director.

Senator Cory Booker added that the first lady "bridges so many gaps in our country because she's so fiercely authentic, and I think that is what we need in this campaign".

Obama's entire speech, which even Trump said was effective, ran only about 12 minutes, but it could be the heart of a stump speech with the potential to confound Republicans.

Barack Obama won 60 per cent of young voters in battleground states, but Hillary Clinton is winning only 52 per cent of them.

"The Obamas can help," said Cornell Belcher, a Democratic pollster. "Particularly among younger, minority voters, what the Obamas represent is something larger than politics. They are iconic figures in a social and cultural sense."