Despite the proximity to power, being vice-president of the United States can be one of the most unglamorous, overshadowed jobs in the galaxy that is official Washington.
Nor is it an automatic stepping stone to the big seat, as a phalanx of aspirants — from Richard Nixon (on his first try right after being Dwight Eisenhower's VP) to Al Gore — can testify.
John Garner, Franklin Delano Roosevelt's vice-president from 1933 to 1941, once said that the job is "not worth a pitcher of warm spit." For many, that description has not changed through the decades even as the current office holder, Republican Dick Cheney, is often seen as one of Washington's premier backstage string-pullers and the architect of the war in Iraq.
Still, the office is imbued with enormous constitutional responsibilities, chiefly as the congressional tie-breaker when called upon and as the heir to the throne should the sitting president die or somehow become incapacitated while in office.
Filling out the ticket, as it is called, can also have serious electoral consequences for tipping potential swing states or balancing off a presidential candidate's perceived weakness. That is why the front-runners to be the No. 2 to presidential rivals Barack Obama and John McCain have been vetted by party lawyers and strategists and chewed over in the U.S. press for weeks now.
Obama, the Democrat, is expected to announce his choice this week and begin campaigning with the chosen candidate on Saturday at Abraham Lincoln's old state capital in Springfield, Ill., where Obama launched his presidential bid.
McCain is expected to name his running mate next week, either during or right on the heels of the Democratic nominating convention in Denver.
Either candidate could pull a surprise running mate out of the hat — it's been done before, most recently when Bill Clinton chose fellow southerner and baby boomer Al Gore to be his VP. Early on, Obama was reportedly flirting with a crossover running mate, Republican Senator Chuck Hagel, a decorated Vietnam War veteran.
McCain's camp, meanwhile, was considering Bobby Jindal, the popular governor of Louisiana and U.S.-born son of Punjabi immigrants.
But below are the names most commonly mentioned. You will notice that the two most prominent female political figures in the U.S. — Democrat Hillary Clinton and Republican Secretary of State Condoleezza Rice — are not on the lists drawn up by the candidates' campaign teams, though both have their very influential backers.
For the Democrats
Joe Biden, senator from Delaware
The "clear front-runner," according to analysts at MSNBC, Biden, 65, brings real inside-Washington and foreign relations experience, two perceived weaknesses of the Obama campaign.
A career politician, first elected in 1972 at 29, Biden has been chair of the prestigious Senate foreign relations committee and recently returned from a fact-finding trip to hot spots Georgia and Ukraine.
His weakness: a career politician who has been in Washington for the past 36 years and from a small state that won't be pivotal on election night.
Kathleen Sebelius, governor of Kansas
An early favourite, she may have fallen off the bandwagon, but she is still a formidable campaigner, known for her bipartisan approach and inclination to take on vested interests, two Obama proclivities as well.
The daughter of a former governor of Ohio (John Gilligan), Sebelius, 60, is one of the most popular governors in America, according to opinion polls. She also hails from a swing state that voted for Bush in 2004.
A vice-presidential bridesmaid, she was considered by the John Kerry campaign to be VP in 2004.
Evan Bayh, senator from Indiana
A youthful looking 52, with a reputation as a straight-shooter if not a charismatic campaigner, Bayh (pronounced Bye) is a second-generation Indiana senator, having taken over the seat of his father, Birch Bayh, in 1999. Before that, he had been governor of Indiana.
A perennial bridesmaid — he was a potential VP for both John Kerry and Al Gore — Bayh would add strong name recognition to the Democratic ticket in a potentially winnable Republican state.
His biggest drawback: he was an early and ardent supporter of the war in Iraq and the Democrat who co-sponsored the bill authorizing the U.S. invasion.
Tim Kaine, governor of Virginia
A working class guy who went to Harvard and became a lawyer as well as (briefly) a Catholic missionary in Honduras, Kaine, 50, has only been governor of Virginia for three years. Prior to that, he was mayor of Richmond, Va.
A tough-minded cost-cutter who has taken on the unions by supporting right-to-work legislation, Kaine is a fiscally conservative Democrat, which may be the message Obama wants to send should he choose him.
The drawbacks: Kaine's nomination might not sit well with big city unions, who are strong Democratic party supporters, and he hails from a small, electorally inconsequential state.
For the Republicans
Mitt Romney, former governor of Massachusetts
Because he is a Mormon whose religion caused a stir in the presidential primaries, a Romney appointment would be a bit of a gamble for John McCain. But it would signal he is willing to put past feuds aside and broaden his tent in unconventional ways.
A very wealthy former investment banker with strong name recognition in the liberal northeast as well as in Utah, where he headed up the successful Salt Lake City Winter Olympics in 2002, Romney, 61, brings real Wall Street heft to a Republican ticket, which may be especially important if this election is all about the economy.
His downsides are his Mormonism, which rankles the religious right in the U.S., an important Republican voting bloc, and the fact that he is more of a Wall Street than a Main Street campaigner.
Tom Ridge, former governor of Pennsylvania
Once the rising, do-everything star of the Republican party — the one picked to head up the new Homeland Security department in the aftermath of 9/11 — Ridge, 62, is a former Vietnam veteran with an impeccable reputation in a key battleground state.
An early front-runner for the job, speculation has diminished recently because he supports abortion rights, which could cause Republican voters on the ultra-religious right to stay home.
One partisan drawback: while Ridge left Homeland Security before the Hurricane Katrina fiasco, he was the one who built it up to the stupendous bureaucracy it has become.
Tim Pawlenty, governor of Minnesota
The least well-known of the potential vice-presidential candidates by far — and one of the youngest — Pawlenty, 47, is a two-term governor, first elected in 2002.
A lawyer who is said to have an easygoing, down-home style, Pawlenty may be the compromise choice and has a number of attributes: he's young, reform-minded, with no serious detractors and is popular in an important swing state.
But he may also not be enough of a political animal. He is said not to have much of a political machine and wasn't able to deliver Minnesota to McCain during the primaries despite McCain's pre-eminence at that point.
Joseph Lieberman, Independent senator from Connecticut
An unlikely choice, granted, but his name will not seem to go away. A former Democrat who was Al Gore's vice-presidential candidate in 2000, Lieberman is, like McCain, a respected, aging (66), battle-scarred maverick who, if selected, would have the rare distinction of being the vice-presidential standard-bearer for both old-line parties as well as the only Jewish one.
A fiscally conservative senator from upscale Connecticut, Lieberman is a convincing orator who would help McCain gain entry into the New York power circles. But he wouldn't help much with the ultra-right Republican base.