Donald Trump challenges legitimacy of election

He began this month with $75 million in his campaign and joint party accounts

A beleaguered Donald Trump sought to undermine the legitimacy of the US presidential election today, pressing unsubstantiated claims the contest is rigged against him, vowing anew to jail Hillary Clinton if he's elected and throwing in a baseless insinuation his rival was on drugs in the last debate.

Not even the country's more than two centuries of peaceful transitions of political leadership were sacrosanct as Trump accused the media and the Clinton campaign of conspiring against him to undermine a free and fair election.

"The election is being rigged by corrupt media pushing completely false allegations and outright lies in an effort to elect her president," he said, referring to the several women who have come forward in recent days to say that Trump had groped or sexually assaulted them. He has denied the claims, calling the women liars.

Earlier today, Trump took to Twitter to warn that "100 per cent fabricated and made-up charges, pushed strongly by the media and the Clinton Campaign, may poison the minds of the American Voter. FIX!"

"Hillary Clinton should have been prosecuted and should be in jail," he added. "Instead she is running for president in what looks like a rigged election."

In a country with a history of peaceful political transition, his challenge to the election's legitimacy as a way to explain a loss in November, should that happen was a striking rupture of faith in American democracy.

House Speaker Paul Ryan, whose decision not to campaign for Trump angered the GOP nominee, made clear he does not share the candidate's concern about the election's legitimacy.

"Our democracy relies on confidence in election results, and the speaker is fully confident the states will carry out this election with integrity," said AsheLee Strong, speaking for him.

It was not the first time Trump has raised the idea the election is unfairly tilted against him, but it has become a resurgent theme for the New York billionaire and many of his supporters in the past several days as he's slipped in preference polls and faced allegations of sexual misconduct.

As well, campaign money is tight, at least in comparison with his rival's resources, according to information that pre-dates the release of a 2005 video that showed him bragging about imposing himself on women.

Trump began this month with $75 million in his campaign and joint party accounts, he said today in a statement.