Common wisdom dictates that the vice president should provide balance to the ticket by representing a different part of the country, another set of experiences, or a basketful of electoral votes.
When I served on the committee that advised Arkansas Gov. Bill Clinton on choosing a running mate in 1992, he gave us only one piece of guidance: "I want someone who can be president." So all candidates were carefully vetted.
When Governor Clinton met with Sen. Al Gore of Tennessee, the two clicked. Senator Gore was from a neighboring state and another progressive Southern politician. He provided a mere handful of electoral votes. Rather than broadening Clinton's constituency, the two men overlapped and reinforced each other. But Gore added one important dimension – a degree of gravitas aided by his foreign policy experience.
Barack Obama's choice of running mate has to be his alone. What can he learn from 1992?
The presumptive presidential nominee must have trust in his running mate, no matter who he or she is, and that person has to be carefully vetted. The vice presidential candidate does not usually make much difference at the polls. But that may be changing as voters become more aware that the understudy must be ready to take over if needed.
That's why Sen. Hillary Rodham Clinton may be the wisest choice. Senator Clinton's constituencies – women and working class voters – would bring the finishing touch to Senator Obama's ticket. And as an older, more experienced person, she may also bring a level of gravitas, not unlike what Gore provided for Bill Clinton.
She has the further advantage of having been thoroughly vetted by the media and by some 18 million voters. Within a hair's breadth of winning the nomination herself, she showed that a sizable constituency considered her qualified to be president – the ultimate litmus test for a vice presidential candidate.
Clinton's priorities were extraordinarily similar to Obama's, making it likely they would reinforce each other rather than compete.
The disadvantages ,though, of Clinton as VP are almost as obvious as the advantages: Can she be effective in second place? Can she support his agenda as enthusiastically as she did her own? Some say she represents old politics, contradicting his campaign theme of change. They can't forget some of the tough words she hurled at Obama during the primary battle. Then there is the trust factor. Can Obama and Clinton be at ease with each other, both on stage and off, both on the campaign trail and in the White House?
And then there is the recurring question, "What about Bill?"
Choosing a running mate is the first decision that the presumptive party nominee makes. It gives us a clue about his judgment, his capacity to reach out, and his vision for the country. Voters are keenly interested in the message that this selection sends.
Could it happen between Obama and Clinton in 2008? Their first public meeting with supporters in Unity, N.H., indicated that they could share the limelight amicably. And the country might just be ready for such a nontraditional ticket.
Some voters will, of course, oppose such a ticket because of race or gender or both. But others would be drawn to the polls for the same reason: An opportunity to vote for the first African-American and first woman – making history on two fronts.
There is something about running mates that creates a shared portrait; one that is larger than the sum of their parts. That electricity was apparent when Bill Clinton introduced Gore at the governor's mansion in Little Rock, Ark., in the summer of 1992. A magical chemistry emerged when they were together. They became a dynamic team, representing new leadership.
When I imagine the red, white, and blue balloons floating down from the convention hall ceiling on Obama and Clinton, both raising their arms high in a victory salute, that picture definitely shouts "change!" It would bring symmetry to African-Americans and women, two constituencies who often went their separate ways during the primary.
Clinton and Obama have already established a unique bond, having gone through the same trial by fire, revealing much about who they are – not only to the voters, but to each other.
In order for the union to work, Clinton will have to be offered a clearly defined portfolio of responsibilities.
Obama has campaigned as a politician who is different from the mold. Moving into the general election, he has increasingly revealed that he is also a political pragmatist who wants to win.
If, after he has vetted all the others, he concludes that he can work in partnership with her and that she would increase his likelihood of winning, he should pop the question.
• Madeleine M. Kunin is the former governor of Vermont, former US ambassador to Switzerland, and author of "Pearls, Politics & Power: How Women Can Win and Lead." She served as co-chair for Hillary Clinton's presidential campaign in Vermont.