 The president can't be everywhere. Even Donald Trump can't be everywhere. So you've got to be a person he can trust, he can rely on to actually advance the agenda. That's the most important job. Of course, if something, God forbid, happens, you've got to be ready to step into that office. That's one of the most important roles of the vice president. Mr. Vance will set out his own ideas when he speaks to the convention on Wednesday. But the highlight of the week will be Thursday night when Donald Trump himself takes to the stage.