The Daily Telegraph By

President Barack Obama has admitted for the first time that Donald Trump could succeed him and advised Hillary Clinton to "run scared" as she prepared to become the first female nominee of a major US political party.

Mr Obama had previously maintained that Mr Trump would never reach the White House but, as the billionaire led in polls, he said it was now "possible" the Republican may win.

The warning came as Mrs Clinton was due to make history at the Democratic Party convention in Philadelphia tonight (Thursday). She planned to use her acceptance speech to put gender at the centre of her campaign, framing the election as a chance to punch the "final crack in the highest glass ceiling".

But 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."

Mr Obama, who was due to address the convention last night, went on to attack Mr Trump for lacking a "basic knowledge about the world", including not understanding what a nuclear triad was, or the difference between Sunni and Shia Muslims.

The issue of gender had been largely absent from the Democratic primary campaign as Mrs Clinton struggled to connect with young female voters, many of whom sided with her left-wing rival Bernie Sanders.

But her advisers said she would now seek to make contrasts between herself and Mr Trump, hammering home to voters sexist comments he had made. In a message to supporters before her speech Mrs Clinton said: "If there are any little girls out there staying up late to watch, I may become the first woman president but one of you is next."

Delegates were shown footage of Amelia Earhart, the first woman to fly solo across the Atlantic. Meryl Streep, the Oscar-winning actress, took to the stage and punched her fists in the air. She said: "What does it take to be the first female anything? It takes grit and it takes grace." Campaign insiders said Mrs Clinton planned to use her speech to "reintroduce" herself to the nation.

In a recent poll 68 per cent of Americans regarded her as "dishonest", more than distrusted Mr Trump, while more than half the country said they viewed Mrs Clinton "unfavourably".

The effort to rebrand her image included an emotional convention speech by her husband, former president Bill Clinton, who described his wife as a champion of families and children.

But even some Democrats dismissed the attempt to recast Mrs Clinton's image. Liz Maratea from New Jersey, a Democrat, said: "Why can't we have somebody in the White House that doesn't need to be shined up? Nothing needs to be repackaged about Bernie Sanders." John Feehery, a Republican strategist, said it was too late to rehabilitate her: "You only get one decade to make a first impression."