Until very recently, there was an assumption that, on the Democrat side at least and barring accidents, the candidacy was decided. Al Gore, Vice- President during Bill Clinton's two terms, who will be only 52 at the time of the next election, would be the Democrats' choice. That, it was believed, was the deal when Mr Gore agreed to run for vice-president in 1992.
But it is not a foregone conclusion. Lacklustre speeches and diplomatic misjudgments from Mr Gore, plus Clinton scandals, could negate the Vice- President's advantage.
If there is to be a contest, however, one aspiring candidate is trying harder and earlier than the rest. He is Richard Gephardt, the 56-year- old leader of the Democrat minority in the House of Representatives. A native of St Louis, a lawyer by training and now a powerful, if sometimes irascible orator, his first bid for president, in 1988, ended in scornful charges that he lacked "substance, ideas and eyebrows".
In the past two months, Mr Gephardt has sprung back into the limelight with a vengeance by the simple, but highly effective method of striving to put as much of what certain British politicians would call clear blue water between himself and Bill Clinton as is politically possible. In doing so, he has taken up a deliberately populist stance on a set of issues that Mr Clinton sees as hallmarks of his presidency - neatly positioning himself to oppose Mr Clinton's heir apparent.
As Mr Clinton prepared for his recent trip to Mexico, the first by a US president since Jimmy Carter, Mr Gephardt took every opportunity to criticise the 1994 North American Free Trade Agreement (Nafta) that Mr Clinton was setting out to defend. For Mr Clinton, Nafta was saving US jobs, stemming Mexican immigration and helping to clean up industrial pollution along the US southern border. A long-time opponent of Nafta, Mr Gephardt denounced its effects as having brought about a disastrous fall in wage levels in the southern states, having encouraged illegal immigration and having done nothing to reduce pollution.
Last week, Mr Gephardt again marked his difference by opposing Mr Clinton's balanced budget, which has a timetable of five years, to 2002. After weeks of wheeling and dealing, Mr Clinton finally clinched the bipartisan agreement he sought. Richard Gephardt declined to budge. The disadvantages of signing up to a deal that went into the next presidency clearly overrode whatever blandishments he may have been offered.
This week, Mr Gephardt played his third card. In a speech to the Detroit Economic Club on Tuesday, he argued strongly against the renewal of most favoured nation trading status for China, citing human rights abuses by Peking.
Mr Clinton has already said he will renew the status, and Congress is limbering up for its annual fight on the subject, with opinions running high because of the party funding scandal in the US which implicates mainland Chinese interests, and the imminent handover of Hong Kong.
As with Nafta and the budget, Mr Gephardt and his coterie have no chance of defeating Mr Clinton's declared policy on China. Because Mr Clinton lacks a majority in either the House of Representatives or the Senate, he needs bipartisan agreement for any of his legislation to pass. But this is what gives Mr Gephardt his opportunity.
He can operate as a minority law unto himself without jeopardising the President's (limited) power, with Al Gore tied to Mr Clinton by virtue of his office.
Mr Gore, as if scenting the danger, spent Tuesday in New Hampshire, the renowned first stamping ground of any would-be president.