As John McCain and Barack Obama gear up to select their running mates, the two men must be wary of lessons from past US presidential races.
Although political commentators are often sceptical of the ability of a running mate to swing the vote in a candidate's favour, one thing is certain - they can cause a lot of problems.
Conventional wisdom has it that Obama needs experience and McCain needs youth if they are going to have a shot at the White House: but some presidential choices were far from wise.
Thomas Eagleton stepped down as running mate after just two weeks
Without a doubt the most unsuccessful running mate of all time was Thomas Eagleton.
Facing an overwhelming defeat from the popular President Richard Nixon, democratic candidate George McGovern could not persuade senior Democrats to step up to the challenge.
After being turned down by five or six party bigwigs, he plumped for little known Missouri Senator, Thomas Eagleton, on the basis of his Catholic faith and strident opposition to the Vietnam War, which was raging at the time.
It seems McGovern's campaign team had not done a thorough background check - and the US press soon uncovered a history of mental illness, including two sessions of electro-shock therapy, in the senator's past.
Despite "1,000%" support from McGovern and favourable polling, pressure mounted and after just two weeks in the job, he was asked to stand aside.
McGovern went on to lose the election in a landslide after a dirty campaign from Nixon, which included the the notorious Watergate break in.
Eagleton stayed in the Senate until 1982 and ended his days as a lawyer and professor in St. Louis, where he was honoured with a star on the St Louis Walk of Fame.
Quayle's career was blighted by a misspelled potato
Dan Quayle successfully campaigned at George Bush's side in the 1988 presidential run-off and served for four years as vice-president of the United States.
Always prone to making gaffes, Quayle was famed for his seemingly meaningless remarks, for instance his statement that "for NASA, space is still a high priority".
The turning point in his political career can be traced to Munoz Rivera School on 15 June, 1992.
After being chosen as Bush's running mate in his 1992 re-election campaign, Quayle was taking part in a spelling competition photo-call.
A child was asked to spell "potato", which he did correctly, but Quayle had it misspelled on his cue card and insisted the child add an "e" to the word.
Already perceived as an intellectual light-weight by large section of the press, the potato slip-up turned him into a national joke.
Bush lost his re-election bid in 1992 to Bill Clinton, and Quayle left politics.
Still popular with conservative grass roots supporters, he campaigned to be the Republican presidential candidate in 2000 but pulled out after an eighth place finish in the first ballot.
Quayle is now a chairman of a private equity firm and writes a syndicated column in the US press. He is the only vice-president in US history to have a museum dedicated to him.
A tax scandal fatally damaged Geraldine Ferraro's reputation
Geraldine Ferraro is the first and, as yet, only female vice-presidential candidate in US history.
She was chosen by Democrat candidate Walter Mondale in his race against Ronald Regan in the 1984 and at first appeared to be a great success - levelling out a long standing deficit in the polls.
But her reputation was fatally damaged by husband John Zaccaro's supposed shady business dealings.
Revelations of his tax avoidance and rumours of Mafia connections led to a steady stream of bad publicity.
When the facts came out Ferraro was cleared of any serious wrongdoing, but the scandal took its toll on the Democratic campaign and Mondale lost the election by a landslide.
After an eight-year break from politics Ferraro sought election to the Senate in 1992 and again in 1998, but the scandal of 1984 overshadowed her political comebacks and she failed to be elected.
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