The comments came after the host asked Biden about the recent Georgia primary election which resulted in long lines for voters after issues with both in-person voting and vote by mail requests.
Biden said access to voting was his “single greatest concern,” and was critical of Trump’s efforts to discredit the use of mail-in ballots--a method of voting the president himself had used.
“This is a guy who said that all mail-in ballots are fraudulent, voting by mail, while he sits behind the desk in the Oval Office and writes his mail-in ballot to vote in the primary,” Biden said.
While Biden had previously suggested Trump might attempt to delay the general election, the comments from Biden articulate the most direct warning from the former vice president as the campaign continues to ramp up ahead of November.
The Democratic presidential nominee also told the late night host that he is “absolutely convinced” that the military will "escort" President Trump from the White House if he refuses to leave, alluding to the recent scathing criticism of the commander-in-chief from top former military officials like former Defense Secretary James Mattis and former White House Chief of Staff John Kelly.
“You have four chiefs of staff coming out and ripping the skin off of Trump, and so many rank-and-file military personnel saying, ‘Whoa, we're not a military state. This is not who we are.’ I promise you, I'm absolutely convinced they will escort him from the White House with great dispatch,” Biden said.
White House press secretary Kayleigh McEnany dismissed Biden’s comments that President Trump would have to be escorted from the White House if he loses in November.
“I think that's a ridiculous proposition. This president is looking forward to November, this president is hard at work for the American people. Leave it to Democrats to go out there and grandstand and level these conspiracy theories,” McEnany told Fox News Thursday morning.
Her comments were echoed by Trump's campaign.
“This is just another brainless conspiracy theory from Joe Biden as he continues to try to undermine confidence in our elections. It was the Obama Administration that tried to subvert an election by spying on the Trump campaign in 2016 and Biden himself was part of the effort to sabotage the incoming Trump Administration because they couldn’t live with President Trump’s victory," Trump campaign communications director Tim Murtaugh told ABC News. "President Trump has been clear that he will accept the results of the 2020 election.”
Biden’s campaign was highly critical when Tuesday’s primary election in Georgia was marred by long lines, voting-machine issues and problems with absentee ballot requests, issuing a statement urging immediate preparations for a November election that has states scrambling to formulate a safe and efficient way to vote in the midst of a global pandemic.
"Free and fair elections are the cornerstone of our democracy. What we see in Georgia today, from significant issues with voting machines to breakdowns in the delivery of ballots to voters who requested to vote absentee, are a threat to those values, and are completely unacceptable,” Rachana Desai Martin, Biden for President National Director for Voter Protection, wrote in a statement released Tuesday.
President Trump has consistently claimed, without evidence, that attempts to expand voting by mail will lead to widespread fraud, and argued weeks before the 2016 election that the contest was “rigged” against him.
Biden said Wednesday that his campaign was putting together a “major” legal initiative across the country to monitor and counteract any attempts to interfere with ballot access.
“What do you think that this is about with Trump? This is a major deal,” Biden said, also referencing the slow pace of vote counting in the state of Pennsylvania that could be another harbinger of chaos in November.
ABC News' Jordyn Phelps and Will Steakin contributed to this report.