Trump plans to challenge US election result as soon as polls close
"As soon as the election is over, we are going in with our lawyers," Trump told reporters ahead of a rally in North Carolina.
Trump has repeatedly attacked the Supreme Court in recent days for not blocking the counting of late arriving ballots for days after 3 November.
Read also: Interview: Everything you wanted to know about Arab-American voting intentions
Trump also defended the "patriots" who surrounded a Joe Biden campaign bus in Texas, with the FBI now investigating the incident.
The democratic presidential nominee denounced on Sunday the alleged harassment of one of his campaign buses by Trump supporters on a Texas highway.
Videos and images posted on Twitter appear to show multiple trucks with Trump flags surrounding and slowing the Biden/Harris bus.
The president himself tweeted a video of the incident late on Saturday, saying, "I LOVE TEXAS."
Democratic officials said the bus, carrying state congressional candidate Wendy Davis, stopped its journey and cancelled two planned events and a news conference, citing "safety concerns".
"We've never had anything like this - at least we've never had a president who thinks it's a good thing," Biden told supporters in Philadelphia on Sunday.
"Folks, that's not who we are. We are so much better than this," Biden said.
Trump slammed the FBI investigation on Twitter, insisting "these patriots did nothing wrong.
"Instead, the FBI & Justice should be investigating the terrorists, anarchists, and agitators of ANTIFA, who run around burning down our Democrat run cities and hurting our people!" he said.
Trump and Biden, who are both running for president, have one last chance to make their case to voters on Monday, the final full day of the campaign that has laid bare their dramatically different visions for tackling the country's pressing problems.
More than 93 million people have already voted and it could take longer than usual for elections officials to process the historic surge in early and mail-in ballots.
Follow us on Facebook, Twitter and Instagram to stay connected