was not unprecedented.

Mr Giuliani said that while the peaceful transfer of power was important, so too was the "accuracy of the election". He said that if the result was close, the campaign would not accept it.

He compared the situation to the contested result in 2000, when George W Bush beat Al Gore. "Al Gore didn't accept it, did he? He went to court over it," he said.

What happened with Al Gore?

Image copyright Getty Images Image caption US presidential candidates George W Bush (left) and Al Gore in 2000

The contest between Mr Gore, a Democrat, and Republican candidate George W Bush in 2000 was one of the closest contests in the nation's history.

The result hinged on the state of Florida, where a narrow margin of victory led to numerouslawsuits and weeks of legal battles, triggering a recount.

The argument reached the US Supreme Court, which put a stop to the recount. The contested votes were eventually awarded to Mr Bush, granting him victory.

Mr Gore, who won the national popular vote by a margin of more than 500,000 but narrowly lost in Florida, finally conceded defeat on 13 December 2000.

"Tonight, for the sake of our unity as a people and the strength of our democracy, I offer my concession," he said.

So what can Mr Trump do?

Mr Trump's options are limited. As with Mr Gore, if the result is too close to call he will have the legal right to contest the outcome and demand a recount.

If he believes that electoral fraud has taken place, he can issue lawsuits