Hillary has cased herself as protector of Obama's policies

US Democratic Party front-runner Hillary Clinton could have President Barack Obama, who remains popular at end of his eight-year presidency, as a secret weapon in her presidential run, a report said on Sunday.

There is no one better positioned to unify the party behind Clinton as her long and sometimes bitter struggle with primary rival Senator Bernie Sanders draws to a close, Xinhua news agency cited the report.

Indeed, Obama retains immense popularity with the Democratic base, including vital groups such as young people, with whom Clinton has struggled, the report noted.

Obama's approval ratings have been marching upward since the start of the year, and the latest Gallup' s daily tracking poll showed 52 percent of adults approving of Obama's job performance and 44 percent disapproving.

Obama can play "a huge role" in bringing the Democratic base and independents together to unite behind Clinton's candidacy, Democratic strategist Jonathan Rosen was quoted as saying.

That could be particularly important as the primary season has shown that Clinton has failed to thrill some parts of the Obama coalition, such as younger voters, the report said.

Though Clinton tried to keep distance from Obama at the early months of her campaign, she shifted the position as the challenge from Sanders became more serious.

Clinton has cased herself as the protector of Obama' s signature domestic achievement, the Affordable Care Act. And a Clinton campaign ad on gun control featured the candidate saying "I'm with him (Obama)".

Part of Clinton' s pivot was clearly aimed at stopping the Sanders insurgency, but her political proximity to Obama could pay dividends in the general election too, the Hill report said.

Clinton will also face a tough challenge in the presidential race as traditionally it has been difficult for a candidate to win the White House after his or her party has held the presidency for the preceding eight years,

But experts said that 2016 could be exceptional due to the polarizing nature of the Republican nominee, brash billionaire Donald Trump, who could leave some voters seeking a "safe haven" with Clinton.

And Obama's popularity could also help counteract Clinton's low favourability numbers, as well as the traditional voters' reluctance to give a party three successive White House terms.

The challenge to win a third term of presidency for the Democratic Party can be overcome "when you have a popular sitting president", Democratic strategist Evan Stavisky was quoted as saying.