BARACK Obama has sensationally admitted Donald Trump “could win” and advised Hillary Clinton to “run scared”.

Just hours before hailing the Democrat as the best qualified candidate ever to become president, President Obama conceded it was “possible” that Republican Trump could win the race.

6 Barack Obama warned that in this unpredictable political climate, Trump could win Credit: Getty Images

Mr Obama's warning comes as Mrs Clinton was due to make history at the Democratic Party convention in Philadelphia tonight as she prepares to become the party’s first-ever female candidate.

Mr Obama said: "It is the nature of democracy that until the votes are cast, and the American people have their say, we don't know [who will win].

“I have seen all kinds of crazy stuff happen and I think everybody that goes into campaigns not running scared can end up losing."

6 Obama endorsed Clinton in a a barnstorming speech last night at the Democratic Convention Credit: EPA

6 Obama's speech went down a storm with the party faithful as he called Hillary the most qualified person for the job Credit: Getty Images

It came as a poll revealed the billionaire businessman had opened up the biggest lead yet on his Democrat rival by 47 per cent to 40.04 per cent - his largest margin yet in the presidential race.

It is believed Mr Trump is benefiting from the post party convention bounce while his rival is still suffering from the "extremely reckless" use of private email to conduct government business.

President Obama had been speaking ahead of his address to delegates last night in which he tore into the real estate tycoon.

And he told the cheering crowd in Philadelphia: “The Donald is not really a plans guy, he is not really a facts guy either.”

6 The pair struck an upbeat tone at the party convention in Philadelphia Credit: Reuters

6 Obama hugged Clinton before holding her hand aloft Credit: Reuters

6 Clinton served under President Obama as US Secretary of State Credit: Reuters

Obama was given a standing ovation when he took to the stage and said of Trump: “He calls himself a business guy which is true, But I have to say I know plenty of business men and women, who achieve success without leaving a trail of lawsuits and unpaid workers and people feeling that they have been cheated.

“Does anyone really believe a guy who has spent his years on this earth showing no regard working people is suddenly going to be your champion?”

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And he accused Trump of selling the American people short with his policies and negative views of the US.

Speaking warmly of Clinton, who became the first woman to represent a major party in the race for the White House on Tuesday after her nomination he backed her saying: “There has never been a man or women , not me not Bill (her husband) , not nobody, more qualified to served as president of the United States of America.”