"This election was rigged and we can't let that happen," Trump said. "We won Pennsylvania by a lot. And we won all of these swing states by a lot."
"Anybody watching television the night of the election was saying 'Wow, I was called by the biggest political people, congratulations, sir, on a big win. And all of a sudden ballots were dumped all over the place and a lot of horrible things happened," he continued.
Trump's lawyers have so far not produced any substantive evidence of fraud and national election officials say there was none.
Biden won Pennsylvania by a margin of 80,000 votes on November 3, helping him assemble a convincing nationwide victory and making Trump a one-term president.
On Monday, Pennsylvania Gov. Tom Wolf (D) formally signed off on the state's certification declaring Biden as the winner.
"It's a disgrace that this is happening to our country. We won this election by a lot. We got 74 million votes," Trump said Wednesday.
"They have to turn over the results," he later added.
Trump, who tore up countless norms during his four years in power, is carving out new territory with his refusal to concede to Biden, while supporters suggest he is already eying an announcement of running for president again in 2024.
Building his brand ahead of a new campaign might be one explanation for the real estate tycoon's dogged pursuit of such a lost cause.
Giuliani and other Trump lawyers have seen baseless challenges to the vote counts thrown out by courts across the country.
And while Trump is alleging -- among other evidence-free conspiracy theories -- that voting machines deliberately deleted millions of his votes, the government election security agency declared this "the most secure" election in US history.
After coming under pressure from a slowly building trickle of senior Republicans, Trump on Monday ended his blockade of government assistance to ease Biden's preparation for assuming the presidency on January 20.
But Trump has yet to take even the simplest steps in normal post-election protocol, starting with a phone call to Biden.
"No, I have not heard anything from President Trump," Biden told NBC News.
Given Trump's threats before the election not to recognize the results, Biden told NBC he is "not surprised by the response of the president."
Since the election, Trump has largely disappeared from his usual work schedule and has not once taken questions from journalists.
However, adding to the sense that he is focused on preparing his next political act, he continues to raise money from supporters contributing to an "Official Election Defense Fund."
Much of that money does not go to the lawyers promoting his fraud allegations but is instead being funneled into paying off 2020 campaign debts and building a future war chest with Trump's political action committee.
Kate Bedingfield, a Biden spokeswoman, said the outgoing president was now the last person to accept the reality of the election.
"Virtually everyone on Earth has accepted that truth except for Donald Trump and Rudy Giuliani," she said.
"The Trump campaign has been laughed out of every courtroom, with their meritless and baseless lawsuits meant to undermine the will of the American people. This is a sideshow."
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With reporting by AFP
