Both Lincoln and FDR made a point of bringing their rivals and people of different political stripes into their administrations to offer reality checks. That is less true with Biden than with Palin, who is a counterweight to McCain's traditionally more centrist positions.

"In the corporate world, really effective leaders are comfortable surrounding themselves with people who may have very different viewpoints," says Stuart Youngblood, a professor of management at Texas Christian University.

"If the vice president were to model the behavior of a v.p. in a corporation," Youngblood says, "it would be: When they go into a room together they can differ all they want, but they better come out of that room and support each other."

Comparing American government to American corporations has become fashionable in recent years.

Such analogies cast the president as CEO and the vice president as ... what? Given that most companies have multiple v.p.s, each with specific duties, where is the comparison most apt? Nowhere, says James O'Toole, co-author of "Transparency: How Leaders Create a Culture of Candor."

"The job of the vice president is not analogous to any job I can think of that exists in the corporate world," O'Toole says. "There is no job in which you stand around waiting, in which you're the backup quarterback. At least the backup quarterback runs the plays in practice. The backup president doesn't do that."

So here, constitutionally, is what the vice president has been charged to do since the 12th Amendment was instituted 204 years ago, putting the two positions on the same ticket rather than having the vice president be the rivalrous runner-up:

• Step in if the president is disabled, incapacitated or dead.

That's pretty much it. Since then, the vice presidency has been awash in possibility and obscurity, in hope and ambitions kept in check. And, "Babylon 5" and "24" aside, the image of a scheming vice president trying to overthrow the chief is not the hallmark of the office today.

Instead, it's a continual fight by a competent, often talented politician to claim relevance and be useful, to prepare for the worst and, in the meantime, be available.

That's been true since 1788, when the office's relevance was asserted in one of the Federalist Papers — albeit after the writer acknowledged that the notion of a vice president "has been objected to as superfluous, if not mischievous."

The author was none other than Alexander Hamilton. Sixteen years later, as he lay on the bank of the Hudson River in Weehawken and contemplated Aaron Burr's bullet in his belly, he might have wished the position didn't exist after all.