Can Clinton unify Democrats?

On June 7, 2008, Hillary Clinton made way for Barack Obama to conquer the White House, conceding defeat after a fractious primary race, and throwing her full weight behind him.

Eight years later, it is she who faces the arduous task of unifying her camp after a -- sometimes bitter -- battle with Bernie Sanders.

On paper, it seems an easier task than the one facing her Republican rival Donald Trump, whose insurgent candidacy and incendiary comments -- dubbed "racist" by leading GOP figures -- are tearing his party apart.

But Clinton's challenge remains very real, with one big question still unanswered: how will "Bernie" behave towards the nominee he fought tooth-and-nail to stop?

The Vermont senator told supporters late Tuesday that "the struggle continues" and vowed to take his message about reforming Wall Street, the minimum wage and the role of money in politics to the Democratic party's convention in Philadelphia next month.

Delivering her victory speech in New York, Clinton did not directly urge her rival to stand down. But she held out an olive branch to him and his supporters.

"Let there be no mistake, Senator Sanders, his campaign, and the vigorous debate that we've had about how to raise income, reduce inequality, increase upward mobility, have been very good for the Democratic Party and for America," she said.

"As we look ahead, let's remember all that unites us."

Obama called both Clinton and Sanders on Tuesday to congratulate them, but made it clear that his former secretary of state was the nominee.

The US president was to meet Sanders at the White House on Thursday -- perhaps the first steps towards a unified approach to November.

Tuesday's primaries "are no longer about the nomination. They are about leverage in the peace talks that are sure to follow," the one-time Obama strategist David Axelrod tweeted on Tuesday.

In 2008, Clinton threw her weight unequivocally behind her erstwhile rival, calling for her supporters "to take our energy, our passion, our strength, and do all we can to help elect Barack Obama, the next president of the United States."

This time, Clinton will have to earn the support on November 8 of the young, passionate voters fired up by Sanders' grassroots campaign.

Her biggest hurdle: the sizeable share of Bernie's fans who view the former first lady, senator and secretary of state as calculating and insincere -- echoing the favorite line of attack of her Republican rival Trump.

"Clinton doesn't have the ability to do it alone," argued Larry Sabato, a political analyst from the University of Virginia.

"A sizable minority of the Sanders troops have grown to despise her. Sanders will have to back Clinton repeatedly and with enthusiasm."

Democrats like to point out that the bad blood between the Obama and Clinton campaign teams was considerably worse than that between this year's rival camps -- and that it did not stop them from winning.

They are also counting on Obama himself to enter the race in the role of unifier-in-chief.

According to the latest Gallup poll, Obama's popularity with that segment of the electorate is sky-high -- at 92 percent.