Tonight’s presidential debate will be breaking new ground.  When Joe Biden and Donald Trump face off this evening for 90 minutes it will make history as the first debate between a sitting president and a former president. The debate also comes unusually early in the general election calendar, before the candidates are officially their parties’ nominees. And in a departure from recent presidential debates, tonight’s will be held in a TV studio with no audience and muted microphones when it’s not the candidate’s turn to speak.