In the intervening hours, Mr. Biden attempts to win the presidency without leaving his house.

With the coronavirus outbreak freezing the country’s public life, Mr. Biden has been forced to adapt to a cloistered mode of campaigning never before seen in modern American politics. He was unable to embark on a victory tour after the Democratic primaries or hold unity rallies with onetime rivals like Senators Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts. Instead, the former vice president is in a distinctive kind of lockdown, walled off from voters, separated from his top strategists and yet leading in the polls.