In America, as in Britain, politics takes a rest in summer. By tradition, the US presidential election campaign does not get going until after the first Monday in September in the final year before the November vote. This year, however, the race is already in full swing. This is partly because of the pressing need to raise ever-larger sums of money, forcing candidates to declare early on. Partly it is because, for the first time since 1928, neither Democrats nor Republicans have a sitting candidate and, at a time of intense political polarisation, contenders need early momentum to impress a sceptical electorate. And partly it is because many states, envious of the huge influence of Iowa and New Hampshire, the first two to hold their primaries, are jostling to bring forward their own contests.

So many states have decided to hold their primaries on February 5 that the nominees for the final contest may well be apparent soon after “Tsunami Tuesday”. The danger, however, for each candidate, and especially for the influential pollsters and analysts, is to assume that the race can be virtually called at this early stage. It cannot. The field is still wide open. And US election politics can change extraordinarily quickly – if a candidate’s campaign implodes, if some outside event alters perceptions or if a dominating issue, such as Iraq, changes.

Several things are, nonetheless, already clear. The first is that the Republicans are in trouble. President Bush’s popularity ratings have now reached an almost record low: two years after a triumphant reelection that also swept Republicans into control of both houses of Congress, the Administration is becalmed and the machine that has put seven of the past ten presidents into the White House is creaking. Today only 35 per cent of Americans align themselves with Republicans compared with 50 per cent with Democrats. Important blocs such as the Hispanic vote have been alienated. Domestic scandals, arguments over immigration, the economy, social issues and, above all, Iraq, have divided the party. As a result, none of the putative Republican candidates enjoys full support from the main supporter bases. And although polls put Rudy Giuliani, the former New York Mayor, ahead, with Fred Thompson and Mitt Romney close behind, there are plenty of possible upsets.

Things look more stable on the Democrat side, with Hillary Clinton and Barack Obama far ahead, John Edwards trailing and the party eager to exploit Republican woes. Here too, however, nothing can be assumed. The Democratic-controlled Congress is just as unpopular as the Bush presidency. All the candidates therefore are trying to distance themselves from the party machine – giving hostages to fortune for the final winner.

Bemused outsiders may see little of the internal electoral dynamics, but they will not fail to notice if, as expected, the world’s most responsive democracy reacts decisively to reset the nation’s course. The political pendulum might have swung deep into conservative territory on tax cuts, abortion, immigration or ethical issues such as stem-cell research, just as the US in the 1960s adopted activist liberal policies on the inner cities and affirmative action that provoked a strong counterreaction later. Now, as then, if voters perceive the need for change, the candidates will pick up the signals quickly. The process of renewal is thoroughgoing, chaotic – and at this stage far from predictable.