Joe Biden says his chief worry is that US President Donald Trump will attempt to "steal" the November election, and the Democratic challenger says he's even considered the possibility that the Republican incumbent would refuse to leave the White House should he lose.
Trump's press secretary accused Biden of trafficking in "conspiracy theories".
"My single greatest concern: This president's going to try and steal this election," Biden said on Comedy Central's The Daily Show, which aired on Wednesday night.
He did not specify how he thought Trump might cheat.
Biden was asked whether he's considered what would happen if Trump refused to vacate the presidency in the event he wasn't reelected.
"I have," Biden said, before suggesting that the military could step in to ensure a peaceful transition of power.
"I am absolutely convinced they will escort him from the White House with great dispatch," the former vice president said.
White House press secretary Kayleigh McEnany responded that Biden was taking "a ridiculous proposition".
"This president's looking forward to November," McEnany told Fox News Channel's America's Newsroom.
"This president's hard at work for the American people. And leave it to Democrats to go out there and grandstand and level these conspiracy theories."