(Bloomberg) -- President Donald Trump called into a television program Thursday night to warn of election fraud and assail Joe Biden just before his challenger was to accept the Democratic nomination.

“This is going to be the most fraudulent election in history,” Trump told Fox News host Sean Hannity, saying mail-in voting will lead to widespread cheating, even though there’s been no evidence of that in prior elections. “They’re trying to steal the election.”

Trump’s interview was timed to counter-program the conclusion of the four-day Democratic National Convention, where Biden is set to deliver a prime-time speech Thursday.

Earlier in the day, Trump traveled to Pennsylvania to criticize Biden from a town next to the Democrat’s birthplace. Biden was born in Scranton before his family moved to Delaware for work when Biden was a child.

Trump said on Fox that 401(k) retirement plans would sink if Biden wins. “They will go down 40 or 50% if he gets in,” Trump said.

Trump also said Biden is doing the bidding of his party’s left wing, and questioned why the nominee hasn’t taken more questions from reporters.

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