 Tonight's presidential debate at 9 p.m. Eastern will be breaking new ground. White House correspondent Greg Cluxton explains. 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 party's nominees. And in a departure from recent presidential debates, tonight's will be held in a TV studio with no audience,