Obama has asked Jim Johnson, former head of mortgage giant Fannie Mae, to begin research on potential candidates for the No. 2 slot on the ticket, media reports said. Johnson performed a similar task for Democratic presidential nominees John Kerry in 2004 and Walter Mondale in 1984.
Here is a list of some possible Democratic vice presidential candidates, in alphabetical order:
- Joseph Biden, 65 - The senator from Delaware, chairman of the Senate Foreign Relations Committee, is a respected foreign policy expert who would give Obama authority on the issue. But Obama might not want to add a second senator to the ticket, and could be looking for a fresher face to reinforce his message that this election is about change and the future.
- Wesley Clark, 63 - A retired Army general and former NATO commander who ran unsuccessfully for the presidential nomination in 2004, Clark is a supporter of Hillary Clinton who could help rally the party and provide a boost on national security issues. But he did not run a strong campaign in 2004 and he would be unlikely to generate much enthusiasm among party activists.
- Hillary Clinton, 60 - Polls have shown strong Democratic support for a "dream team" ticket of Obama and Clinton, his top rival for the nomination. Obama has not ruled out the option, which would help unify the party after a grueling nominating battle. But Clinton also would bring complications, including the return of former President Bill Clinton to the White House. A joint ticket could help attract some of Clinton's supporters -- including women and white working-class Democrats -- who have been reluctant to support Obama.
- Chris Dodd, 64 - The Connecticut senator, a fluent Spanish speaker and expert in Latin American issues, is the chairman of the Senate Banking Committee and a former foe for the presidential nomination who quickly endorsed Obama after dropping out. He would help bolster Obama's foreign policy and economic credentials, but presents many of the same drawbacks as Biden.
- Chuck Hagel, 61 - The Republican senator from Nebraska, a conservative Vietnam veteran but outspoken critic of the Iraq war, would help Obama reach out to independents and Republicans and reinforce his promise to bridge partisan divides.
- Tim Kaine, 50 - The Virginia governor was one of Obama's earliest and strongest supporters and could help him in a state that traditionally has been Republican in presidential elections but has been turning Democratic in recent years.
- Sam Nunn, 69 - The former Armed Services Committee chairman from Georgia is a respected foreign and military policy voice, but his age and conservative view on some social issues might make him an awkward fit with Obama.
- Ed Rendell, 64 - The Pennsylvania governor has been one of Clinton's strongest campaigners and he could help woo her supporters and help deliver a key state. A former district attorney and the mayor of Philadelphia, Rendell has executive experience that could help Obama.
- Bill Richardson, 60 - New Mexico governor, a Hispanic, could help with Latino vote -- the fastest-growing segment of the electorate and a potentially vital voting bloc. A seasoned negotiator, the former energy secretary and U.N. ambassador would also bring foreign policy experience to the ticket as well as inside knowledge of how Washington works.
- Kathleen Sebelius, 60 - Two-term governor of Kansas could bring some vital elements to the ticket: she's a woman and as the leader of a mostly Republican state has shown she can work across party lines. But she is largely untested on the national stage.
- Ted Strickland, 66 - The governor of Ohio is another strong Clinton supporter who comes from a battleground state. A former U.S. congressman, the first-term governor is not well-known nationally.
- Jim Webb, 62 - The first-term Virginia senator, Vietnam veteran and former secretary of the Navy has written seven novels, including "Fields of Fire," considered one of the best novels about the Vietnam War. Webb could help Obama in a state that has turned more Democratic in recent years.