At 81 years old and seeking another four years in the White House, the moments when Joe Biden's off his game take on a fresh resonance after his disastrous first debate.
They fear the former president may make public statements against those who convicted him, inciting his supporters to "identify jurors and threaten violence against them".
This time, in a major first, the candidates will have their microphones cut off while their opponents respond to the first question of each of the debate's six segments.
While last week's presidential debate was mired in interjections and heckling, not even Joe Biden telling Donald Trump to "shut up" was enough to keep him quiet.
Donald Trump could face the most direct challenge of his presidency to his handling of the coronavirus pandemic, the economy and his personal conduct in his first debate against Democratic nominee Joe Biden.
Former Vice President Joe Biden and Vermont Senator Bernie Sanders have cancelled separate presidential campaign rallies as state officials express concern over large indoor gatherings held during the coronavirus pandemic.