|Could Tim Kaine, right, be Barack Obama's pick for vice president? [EPA]
The presidential candidates will pick their running-mate's before the party conventions which begin in one month.
With the Olympics likely to dominate news coverage in the US over the next couple of weeks, both candidates are likely to try to beat the news blackhole by unveiling their deputies.
As the humourist Will Rogers put it, "the man with the best job in the country is the vice-president. All he has to do is get up every morning and say, 'How is the president'?"
Both candidates are likely to consider candidate's from swing states to try to swing them into their camp, but they would be wise to remember that John Kerry lost North Carolina in 2004, his running mate John Edwards' home state.
Also worth keeping in mind is that eight of the US's 42 presidents have been replaced in office by their vice-presidents, the last one being Gerald Ford replacing Richard Nixon in 1974.
The vice-presidential selection teams and an army of lawyers go through potential candidates, everyone from politicians past and present to business leaders to current and former members of the military.
The serious contenders are then given a questionnaire to try to prevent anyone with an embarrassing past from getting through.
After a review by the lawyers, an even shorter list of contenders are asked for even more details about their life and after the lawyers have satisfied themselves, the choice will be made.
So here's a look at some, though not all, of the possible contenders in no particular order.
John McCain is looking for youth, someone respected on the economy, and someone who can appeal to the Republican base and religious conservatives.
Mitt Romney: Remember the rich, handsome Mormon from the Republican primaries? Despite sparring during the debates, Romney and McCain have made friends since the former Massachusetts governor dropped out of the race. Romney was head of the Salt Lake Olympic Organising Committee in 2002, and was widely praised for making the games successful.
|Bobby Jindal, right, would appeal to the
Republican base [GALLO/GETTY]
His family hails from Michigan, a battleground state.
Tim Pawlenty: Young, handsome governor of battleground Minnesota.
He calls himself a "Sam's Club" Republican instead of a Country Club Republican. (Sam's Club is a really US big retailer.)
Pawlenty sees himself as a man of the people not an elitist and even though he's a relative newcomer to the national stage, he plays well to the Conservative base of the party, something McCain hasn't done.
Charlie Crist: Well-tanned, popular governor of battleground Florida. He recently got engaged after 30 years as a bachelor, and not an ultra-conservative.
However, if McCain thinks he's going to take Florida anyway, he may not want to go this way and instead pick someone who will appeal in the other battlegrounds.
Bobby Jindall: Young Indian-American who has only been governor of Louisiana since January.
He served two terms in congress and he's a Catholic convert who is strongly anti-abortion, appealing to the Republican base.
Rob Portman: Former US congressman from Ohio and former US trade representative (in Bush's cabinet, he holds the title of ambassador).
He appeals to the conservative base, but has the Bush White House on his resume, and McCain is conscious of the "McBush" label.
Barack Obama needs somebody with foreign policy experience who could provide some gravitas to the ticket and shares the vision of the Illinois senator.
Tim Kaine: Governor of Virginia, another key battleground state. Terry McAuliffe, the former Democratic National Committee chairman and Hillary Clinton campaign manager stepped in to the race by saying Kaine would be a good pick for Obama.
Could Clinton and Obama form
a 'dream ticket'? [Reuters]
Joe Biden: Long serving senator from solidly Democratic Delaware, chairman of the Senate Foreign Relations committee, former presidential candidate. He has got the gravitas.
Hillary Clinton: Senator from New York, former first lady, fought the primary battle to the bitter end. Her supporters would be thrilled to see her back in the limelight again.
Evan Bayh: Senator from Indiana. Bayh was a popular two-term governor and former Hillary Clinton supporter. That could go a long way with her people.
Kathleen Sebelius: Governor of Kansas, where Obama's mother was from. She is a female Democrat from a mainly Republican state.
Dick Gephardt: Former speaker of the House and former long-time representative from Missouri and also a former presidential candidate in 2004 himself.
Jack Reed: Senator from Rhode Island, another solidly Democrat state. He went to Iraq and Afghanistan with Obama, and he's a veteran.
Source: Al Jazeera