Trump faces uphill battle

Donald Trump will need to deliver the speech of his life on Thursday, outlining his vision for America and seeking to salvage a fractious Republican convention after his chief rival declined to endorse him in his run for the presidency.

The most controversial US presidential contender in modern times will accept the nomination of a Republican Party set up to abolish slavery and which has guided more candidates to the Oval Office than any other.

Nationwide polls put the New York billionaire, who has never held elected office, and Hillary Clinton neck and neck with the former secretary of state heavily criticized over an email scandal.

The four-day Republican convention in Cleveland, which braced for mass and potentially violent protests, has so far passed off with little more than scuffles and a handful of arrests in the streets outside.

But inside the halls, the convention itself has been anything but uneventful. Public spasms of disunity aside, there was the embarrassing revelation that a prime-time speech by Trump’s wife Melania had plagiarised remarks made by First Lady Michelle Obama.

When Trump takes centre stage on Thursday night, watched by millions of Americans on prime-time television, he will need to prove that he is worthy of the White House and capable of being commander-in-chief. He will have to attempt to heal deep party divisions, laid bare late on Wednesday when his chief rival was booed off stage, and somehow overcome concerns about the divisive campaign he has run so far, which has alienated minority voters, women, Muslims and Latino immigrants.

His campaign defied political norms -- fueling racial tensions, offending key voting blocs, eschewing big-spending advertising campaigns and relying on media coverage above campaign structure.

"Mr Trump’s speech will focus on his vision," his campaign manager Paul Manafort told reporters on Thursday, and "deal with current affairs such as the crisis facing cities and terrorism."

In an interview with The New York Times, published on Wednesday, Trump qualified normally sacrosanct support for Nato allies, warning it would depend "if they fulfil their commitments to us."

Trump’s roller-coaster campaign defeated 16 rivals and steamrolled stubborn party opposition after being written off as a joke.

But he now faces the gargantuan task of trying to unify a party torn apart.

On Wednesday, the convention’s rapturous welcome for arch conservative Senator Ted Cruz turned into deafening boos after he provocatively told delegates to "vote your conscience" in November.