Inside John Kerry's (search) campaign brainroom, a vice presidential selection team is weighing many factors as it looks over the dozens of names swirling around as a potential running mate for the presumptive Democratic presidential nominee.

The Kerry camp has been watertight as it secretively goes through its decision-making process, but as it deliberates, some obvious characteristics are under consideration. Among the qualities Kerry's selection team is seeking are personal chemistry with the candidate, ideological similarity or balance and regional balance. The campaign also wouldn't mind a running mate who can win a state or two. Foremost, the candidate must follow the adage of do-no-harm.

A cardinal rule is that the vice president should at least not be a drag, said Larry Sabato, director of the University of Virginia's Center for Politics (search). The candidate must be fully vetted and prepared to run a national campaign.

"You want somebody who knows what he or she is doing," Sabato said.

History shows that presidents have employed a range of strategies when choosing running mates. With Dick Cheney, George W. Bush added experience to the ticket. Bill Clinton and Al Gore came from the same moderate wing of the party and were both from the South, but Gore contributed national political experience to Clinton's executive background. Dan Quayle offered George H. W. Bush youth and ideological diversity, with Quayle's conservative views balancing Bush's more centrist ones.

"Gore strengthened [Bill] Clinton as a senator with a variety of experiences in which Clinton was weak. Cheney provided [experience] for Bush," Terry Madonna, director of the Center for Politics and Public Affairs at Millersville University (search) in Pennsylvania, told

Historians say the most successful example of balancing the ticket is Massachusetts Sen. John F. Kennedy's selection of Lyndon B. Johnson, a Texan. This selection helped the Northerner pick up Texas and other Southern states.

"If you go back through the sweep of American history, the only vice president who actually probably elected a president by virtue of his presence certainly back through the Civil War was Lyndon Johnson," Madonna said.

Earlier this month, Kerry named Washington businessman and civic leader Jim Johnson to lead his vice presidential search team. The Kerry campaign said over the next several weeks Johnson, who served as a staffer to former Vice President Walter Mondale, will build a team to identify and vet potential nominees. Kerry campaign chairwoman Jeanne Shaheen has promised that will be a very careful and through process.

Personal chemistry has sparked some pundits to talk about Kerry's buddy, Arizona Sen. John McCain, a Republican. That same quality casts doubt on the possibility of North Carolina Sen. John Edwards, who ran against Kerry during the primaries and with whom Kerry is not particularly close.

"You have to have the element of personal compatibility. People expect the president and vice president to work hand-in-glove," Sabato said.

Kerry is frequently called a liberal, and to balance the ticket ideologically, choosing a moderate would make sense, say pundits.

But Madonna said the nomination of a moderate would not be enough for Kerry to escape the liberal tag. He also noted that this strategy could be risky. Although the Democratic Party is now united, "the danger is that a bad choice could smash the consensus."

He cited Sen. John Breaux, a Louisiana Democrat, as an example of how that could happen. "He's too conservative," Madonna said.

Sabato sounded a similar warning. "You may think it would help a liberal to put a moderate on the ticket, but you could easily spend a good part of the campaign with the presidential nominee debating the vice presidential nominee. What does this ticket stand for? It sounds good, and yet it could cause a lot of problems."

Choosing someone from a different region would balance the ticket in another way, but the bottom half is unlikely to make a great deal of difference except in the candidate's home state, Sabato said. However, in a close race, winning just one state could make the difference.

"Ideally, you want to find somebody who can carry his or her state. Ideally, you'd like that to be a state that would be a competitive state like Missouri or Florida," Sabato said.

Among the candidates cited as possibilities to carry a swing state are Indiana Sen. Evan Bayh, Breaux and Missouri Rep. Dick Gephardt.

Another characteristic to look for in a running mate is demographic appeal. A woman like New York Sen. Hillary Clinton or a Hispanic like New Mexico Gov. Bill Richardson would fit this bill. But Madonna cast doubt on this strategy, noting Democrats already lead among Hispanics and single women, and Kerry would only "gain marginally by it."

Balance is not the only goal. If Kerry were to add another Vietnam veteran like former Georgia Sen. Max Cleland, as an all-veteran ticket it would be "a confirming effect," Madonna said.

The most practical issue at hand, however, may be selecting a candidate qualified to succeed the president. "You’ve got to pass the presidential muster. The press and the public have to be convinced that the person can succeed to the office if necessary," Madonna said.