KEY POINTS:
Barring some sweeping political tsunami, Democrat Senator Barack Obama will lock eyeball to eyeball with Republican Senator John McCain in this year's presidential debates.
Senator Hillary Clinton still has a white-knuckled, one-fingered grip on Obama's immaculate suit jacket, but her slim chances have narrowed further with his (at least temporary) recovery from the Pastor Wright thunderstorm.
If his voter support had collapsed, if polls had showed her taking commanding leads in the remaining contests, if superdelegates had been spooked en masse into her waiting arms ... then maybe.
But in fact polls show Obama closing on her in Pennsylvania, opening a yawning gap in North Carolina and leading her nationally as he welcomes yet more superdelegates to his flock. And of course he leads in the pledged delegate count, popular vote and states won ... Meanwhile Clinton has floundered through a minefield of "mis-speak" without a flak-jacket and had to shake up her warring staff ... again. And it seems a big ask for the superdelegates to spurn the candidacy of an African American making a historic bid when he's clearly the frontrunner.
So this look at vice-presidential choices for the likely nominees focuses mainly on Obama and McCain.
1) TAKING PITY ON DEFEATED FOES
What happens: The nominee chooses a rival from among the primary field.
The idea: The candidate needs his/her rival's supporters after a close contest, or to appeal to a section of the electorate.
Historical example: Ronald Reagan choosing George Bush snr.
The likelihood - Democrats: Opinions differ wildly as to whether the so-called "dream" ticket of Obama/Clinton could happen. There are several arguments in its favour. Pollsters track a yearning for change in the electorate. There are also difficult economic conditions and a war - which all closely mirrors the factors in play during the Bill Clinton/Al Gore run against Bush snr. Clinton is part of the past as a former first lady but part of the future in the sense of being the first woman with a shot at being president. Maybe it is time to cast caution aside and go for a bravely historic ticket. Secondly, the race has been so tight and gnarly it may be necessary for party unity to have both involved. Thirdly, they may need each other. Apart from a brief period after Super Tuesday when Obama looked to have an inevitable momentum, neither candidate has successfully seduced the other's supporters. Obama has done well in states with large numbers of his people - independents, wealthy whites, university graduates, African Americans, the young.
Historically Clinton's people - whites, women, older voters, blue collar workers - make up a bigger voting bloc and she also appeals more to the influential Hispanic group. Maybe Obama could draw all those people with help from a white male governor ... but maybe not. Clinton's voters will occupy the general election battleground - McCain will be after as many as he can lure. They are more likely to be susceptible to McCain than Obama's folks. But could Obama and Clinton work together? Could she suffer playing second? Could he handle Bill hanging around? When you consider what they each add - tough, practical populism from Clinton and charismatic, big-picture idealism from Obama - it could be a great mix.
The likelihood - Republicans: McCain has several issues to ponder. He has to take his age out of the equation. People cannot be put off voting for him because he will be in his mid-70s during his term. He needs someone youngish, fit and qualified to be president in case he dies in office, but also to prevent photo-ops looking like a still from Grumpy Old Men. Of his vanquished rivals, Mitt Romney has governing and business experience which McCain lacks. He would be enough of a fresh, non-Washington face to add some vibrancy to the ticket. There was no love lost between them as rivals but they have since made up. Romney also excites the conservative underbelly of the party and McCain needs the Republicans enthused and unified. Mike Huckabee is an unlikely choice. He appealed to evangelical conservatives but upset economic conservatives with his tax policies. Rudy Giuliani failed to set the county alight.
2) STRENGTHENING THE DEFENCES
What happens: The nominee chooses someone very different to himself/herself.
The idea: The candidate is trying to reach voters he/she can't and/or to ease concerns about himself/herself or is picking someone who may deliver a tactically important state.
Historical example: Both George Bush jnr and John Kerry balanced and diversified. Bush chose the older government-experienced Dick Cheney to lessen concerns about his own youthfulness and foreign affairs inexperience. Kerry chose John Edwards to give the ticket a southern, everyman appeal since he was seen as an elite, northeastern, Washington-insider, intellectual liberal.
The likelihood - Democrats: Conventional wisdom favours this approach. Because the nominee will represent a major departure from the norm - a woman or an African American - the argument goes that either should be paired with the norm - a white male - to steady quaking voters.
Obama needs is a centrist who can tie-in Clinton's voters to the ticket and make up for his inexperience. Obama is inexperienced at both foreign policy and domestic governance - there's no obvious name who brings both.
Also, Obama has faced criticism by association: To his pastor, former leftwing radicals, Louis Farrakhan and a businessman on trial for corruption. His wife Michelle has been criticised for what were perceived to be unpatriotic comments. Hammering on these fronts could damage Obama's standing with middle America. Perhaps he could do with an older, reassuring figure on the ticket.
Names suggested by pundits have included Senator Jim Webb of Virginia who is a Vietnam vet and former secretary of the Navy under Reagan; Ohio Governor Ted Strickland, the son of a steelworker who is a Methodist minister; Sam Nunn, a former four-term senator from Georgia who chaired the armed services committee; Senator Joe Biden of Delaware who chairs the Senate Foreign Relations Committee; Senator Bob Casey from the strategic state of Pennsylvania and former Senator Tom Daschle of South Dakota. Clinton needs a white male to pacify white male voters, preferably one who can bring a nice juicy state with him. Maybe Strickland or Indiana Senator Evan Bayh, who is also a former governor.
The likelihood - Republicans: McCain needs to appeal to independents and Reagan Democrats on one hand and the conservative rump of his party on the other. His running mate is likely to be more conservative than he is to placate the party since McCain himself has a proven ability to draw independents and moderate Republicans. He also needs someone with governing experience. A candidate with links to one of the key swing states like Ohio, Pennsylvania or Florida would help. And he needs someone young enough to suggest a forward-looking party.
Candidates in the frame include: Minnesota Governor Tim Pawlenty; Tom Ridge, a two-term Pennsylvania Governor and Homeland Security Secretary; Senator Sam Brownback of Kansas; Florida Governor Charlie Crist and South Carolina Governor Mark Sanford.
3) SELECTING A MIRROR IMAGE
What happens: The nominee chooses someone like himself/herself.
The idea: The candidate is trying to reinforce a theme so choosing someone similar reinforces his/her own appeal.
Historical example: Bill Clinton, as a young, fresh-faced governor challenging an incumbent war president went for a young, progressive southerner like himself, Gore, to reinforce his theme of generational change.
The likelihood - Democrats: Since Republicans will label Obama as the second coming of Jimmy Carter, political necessity seems to argue against a youngish, leftie VP but if he does take that route former candidate John Edwards or Ohio Senator Sherrod Brown are possibilities. Clinton and Kansas Governor Kathleen Sebelius are probably the only women in contention. Gore combines a progressive image with experience, but would he want the job again?
The likelihood - Republicans: Conventional wisdom suggests that McCain has foreign policy covered and doesn't need another security expert. However, this isn't a conventional year and McCain may decide to gamble all on the security pitch - "only we can keep you safe" - and go for a tag team approach. Picking someone with a global profile may also be needed to dim the glamorous opposition.
McCain provides the experience, reassurance - he can afford to be bold and pick someone voters could view as an exciting president-in-waiting. Names suggested here include Secretary of State Condoleezza Rice and General David Petraeus. Both have strong negatives: They solidify McCain's link to the unpopular Bush Administration and Iraq. But voters might see Rice - an African American woman - in the VP slot as a compromise to electing Obama, Clinton or both.
4) REACHING ACROSS THE TABLE
What happens: The nominee chooses a partner from outside his/her own party
The idea: Polls have shown voters sick of party warfare in Washington and wanting change and more cross-party co-operation. It would be an extremely unusual move.
The likelihood - both parties: Unlikely but more likely this year than most election years. For a long time it seemed there might be an independent tilt at the White House from New York Mayor Michael Bloomberg.
Obama's twin themes are change and the need for bipartisanship. He has hinted he might appoint a few Republicans to his cabinet - Senators Chuck Hagel and Richard Lugar are likely to figure. Bloomberg, Hagel and former Secretary of State Colin Powell are outside chances.
McCain is close to independent Senator Joe Lieberman, a former Democratic vice-presidential candidate.
