Donald Trump's false claims about voter fraud in the critical battleground of Pennsylvania have raised concerns he could again try to overturn results in the US presidential election.
Opinion polls, both nationally and in seven closely divided states, show former president Trump locked in a tight race with Vice President Kamala Harris just days before the election.
Trump continues to falsely claim his 2020 loss to President Joe Biden was the result of widespread fraud in multiple states that Trump lost, while he and his supporters have spread baseless claims about the election on Tuesday, US time.
Trump stepped up his unfounded allegations that probes into suspect voter registration forms in Pennsylvania are proof of fraud.
Some of his Republican supporters alleged voter suppression when long lines formed this week to receive mail-in ballots.
Harris's Democrats, meanwhile, are preparing for the possibility that Trump could try to prematurely claim victory before all votes are counted, as he did in 2020.
Their initial plan is to flood social media and news media with calls for calm and patience should he do so.
"We are sadly ready if he does and, if we know that he is actually manipulating the press and attempting to manipulate the consensus of the American people ... we are prepared to respond," Harris said in an interview with US broadcaster ABC on Wednesday.
Trump's false claims about voter fraud after the 2020 vote preceded the deadly January 6, 2021 assault on the US Capitol by Trump supporters seeking to halt or sway the congressional certification of the electoral votes that determine who becomes president.
"This is sowing the seeds for attempts to overturn an election," said Kyle Miller, a strategist with the advocacy group Protect Democracy.
"We saw it in 2020, and I think the lesson Trump and his allies have learned since is that they have to sow these ideas early."
Trump's allies also have raised concerns that non-citizens could vote in significant numbers, though there are few examples of that happening.
On Friday, several US intelligence agencies said Russia had created a video circulating online that falsely showed people from Haiti voting multiple times in the state of Georgia.
The video is part of Russia's efforts to undermine confidence in the election and divide Americans, the agencies said.
Georgia's top election official said the video likely came from a Russian troll farm.
A judge extended the mail-in ballot deadline by three days in Bucks County, north of Philadelphia, after the former US president's campaign sued over claims some voters were turned away before a Tuesday deadline.
Election officials discovered potentially fraudulent registrations in two counties, prompting investigations by local law enforcement. There is no evidence the applications resulted in illegal votes.
In Pennsylvania, an activist posted a video of someone dropping off a bin of ballots to the county courthouse and saying it was suspicious; it turned out to be a worker for the United States Postal Service “literally just delivering the mail”, said Pennsylvania Secretary of State Al Schmidt.
The video has been viewed more than five million times on social media platform X.
Trump held a rally in Michigan on Friday and was later due to speak in Wisconsin, while Harris spoke in Janesville in Wisconsin and was due later in Milwaukee for a rally featuring rapper Cardi B.
Senior Harris campaign staff say their internal data shows Harris winning battleground state voters, who have made up their minds in the last week, by double-digit margins.
Trump tells his rallies to expect a big victory on Tuesday, saying he could only envision losing "if it was a corrupt election".
Trump's claims have raised concerns he is preparing to again blame a potential loss in Pennsylvania, the largest of the seven states likely to decide the result of the election, on voter fraud.
"We caught them CHEATING BIG in Pennsylvania," he said in a social media post on Thursday, demanding criminal prosecutions.
