Republican presidential candidate Donald Trump has repeated his claim that the US election is rigged, and the accusation seems to be resonating with voters, despite the fact that he has not offered any evidence to substantiate his statement.

"Remember folks, it's a rigged system," Trump told a Pennsylvania rally on Friday. "That's why you've got to get out and vote; you've got to watch, because this system is totally rigged."

Reuters news agency reported that its presidential polling from October 7-13 showed Democratic presidential candidate Hillary Clinton with a 7-point lead, nationally. The same poll from October 14-20 gave her only a 4-point lead.

Meanwhile, a compilation of national opinion polls, collected by RealClearPolitics, showed Clinton comfortably ahead by 6.2 percentage points - with 48.1 percent support to Trump's 41.9 percent.

Trump is scheduled to make a campaign stop Saturday in Gettysburg, Pennsylvania - the site of a decisive Civil War battle, and cemetery, as well as the place where Republican President Abraham Lincoln delivered, perhaps, his famous address. 

It's unclear if Trump will reiterate his unfounded claim, which has become something of a mantra for the real estate mogul and former reality television celebrity, at a place that is certainly historical and, for some, hallowed ground. Trump campaign aides said he would outline the agenda for his first 100 days in office, should he win the election.

Asked if he would commit to a peaceful transition of power during Wednesday's debate, Trump replied: "What I'm saying is that I will tell you at the time. I'll keep you in suspense. OK?"

Clinton, US President Barack Obama and some Republicans have rebuked Trump for calling the legitimacy of US elections into question.

A threat to democracy

Clinton slammed Trump on Friday as a threat to American democracy for not pledging to honor the results of the upcoming presidential election as the bitter rivals fought for supremacy in battleground states.

The Democrat said Trump's conspiracy theories illustrated his authoritarian tendencies.

"We know the difference between leadership and dictatorship, and the peaceful transition of power is one of the things that sets us apart," Clinton told a rally in Cleveland, Ohio, one of the key swing states up for grabs in the November 8 election.

President Barack Obama also slammed Trump for refusing to say he would accept the election results during the third and final presidential debate this week.

"When you try to sow the seeds of doubt in people's minds about the legitimacy of our election, that undermines our democracy," Obama said at a rally in Miami, Florida, on Thursday, where he was campaigning for Clinton.

"When you suggest rigging or fraud without a shred of evidence, when last night at the debate, Trump becomes the first major party nominee in American history to suggest that he will not concede despite losing... that is not a joking matter."

bik/sms (Reuters, AFP, AP)