WASHINGTON – Joe Biden says his chief worry is that 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.“My single greatest concern: This president’s going to try and steal this election,” Biden said on “The Daily Show with Trevor Noah,” which aired Wednesday night. “This is a guy who said 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 was asked whether he’s considered what would happen if Trump refused to vacate the White House in the event he wasn't.