Lititz, Pennsylvania - Donald Trump doubled down Sunday on his baseless predictions of voter fraud in battleground states as he and rival Kamala Harris launched their frantic final 48 hours of campaigning to court the last holdouts in a bitterly contested US election.

The presidential race is going down to the wire, with more states functionally tied in polls at this point than in any comparable election.

Over 77.3 million people have now voted ahead of Election Day on Tuesday, just over half of the total ballots cast in 2020.

With the hours ticking away, 78-year-old Trump again indicated he may not accept a defeat and he added to his increasingly dark rhetoric by musing to supporters that he wouldn't mind if journalists were shot.

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Democrats are "demonic," he told a crowd in Lititz, Pennsylvania, also telling his own supporters they would be "stupid" if they didn't vote.

The Republican often sprinkles speeches with colorful insults, but the tone has become increasingly apocalyptic and tinged with violence.

Despite no evidence of any meaningful election cheating in the US, he claimed that Democrats in the crucial swing state of Pennsylvania "are fighting so hard to steal this damn thing."

And during his often unfocused 90-minute address, he recalled the near-miss assassination attempt against him in July, adding that for him to be shot again the bullet would have to pass through the crowd of media.

"To get me, somebody would have to shoot through the fake news – and I don't mind that so much. I don't mind that," he said to laughter.

Around the same time, Harris was quoting scripture in a majority-Black church in Detroit, Michigan, and urging Americans to look beyond Trump.

"Let us turn the page and write the next chapter of our history," the US vice president said.

"While we know there are those who seek to deepen divisions, sow hate, spread fear and cause chaos, this moment in our nation has to be about so much more than partisan politics."

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Harris called Trump's accusations of election fraud an attempt to make people feel "their vote won't matter."

"The systems that are in place for this election in 2024 have integrity," she said. "The people will determine the outcome of this election."

Harris also said she had mailed in her absentee ballot to California and was "feeling great" about the 48-hour sprint.

A final New York Times/Siena poll Sunday flagged incremental changes in swing states, but the results from all seven remained within the margin of error.

Harris – desperate to shore up the Great Lakes states known as the "blue wall" seen as essential to any Democratic victory – was spending the day in Michigan, where she also heads to Pontiac and an evening rally at Michigan State University.

Trump's Sunday timetable centered on Pennsylvania, North Carolina, and Georgia, the three biggest swing-state prizes in the Electoral College system that awards states influence according to their population.

On Sunday, Trump made a rare admission to ABC News that "I guess you could lose, can lose. I mean, that happens, right?"

But at his Pennsylvania rally he said that in 2020, when he lost his reelection effort to Joe Biden and then tried to overturn the results, he "shouldn't have left" the White House.