The contrasting strategies of the two figures vying to be president are in the spotlight ahead of the event in Pennsylvania
It was the debate that was never meant to happen.
Donald Trump will take the stage in Philadelphia on Tuesday night to face, not the familiar foe he expected when he agreed to the encounter in May, but an opponent he has never met and has struggled to define; Kamala Harris, the US vice-president, whose emergence as the Democratic nominee has changed the direction, and very nature, of the presidential election.