After 19 months of campaigning as the sole focus of attention, the moment was a telling one for Obama, who is learning to share the spotlight—for better and for worse—with a man whose personality is almost polar opposite of his own.

Historians like to say that chemistry between a candidate and his running mate is of little importance - ultimately the public is electing the nominee, not his sidekick. Certainly recent history is littered with successful tickets that were not exactly in love with one another: Ronald Reagan and George H. W. Bush, Dwight D. Eisenhower and Richard Nixon and John F. Kennedy and Lyndon B. Johnson come to mind. But the last two vice presidents, Gore and Cheney, have changed the way the public views the office by elevating the importance of the role — and, in the process, of the rapport between the two highest office holders in the land.