Leading article: Leaner and meaner, the presidential battles go on

It is only just February and the early primaries have already thinned the vintage field of US presidential hopefuls to just two on either side. With the graceful withdrawals this week of Rudy Giuliani and John Edwards, two initially plausible candidates acknowledged that 2008 was not to be their year. Mike Huckabee remains in the Republican race, but limps far behind the frontrunners.

Mr Giuliani, in staking everything on a late debut in Florida, made a fatal miscalculation. In any other year, his gamble might have paid off. He was unlucky that the races on both sides engaged the voters from the start. This year Iowa and New Hampshire were not provincial rehearsals, they opened the national race proper. He also misread the field. Up against the patriotic heroism of John McCain, the smooth managerialism of Mitt Romney, and the folksiness of Mr Huckabee, Mr Giuliani's claim to be the "mayor of America" did not quite cut through the competition as he had hoped.

Most of all, though, he misread the times. Fear of terrorism, even terrorism of 9/11 proportions, gave way to popular disenchantment with the Iraq war, which is in turn ceding electoral precedence to worries about the economy. This shift might give Mr Romney an edge, were he not such a bland and wooden campaigner. Today's Americans like their president to have character. Senator McCain wins here every time.

Mr McCain is also winning on endorsements. After bowing out himself, Mr Giuliani immediately put his support behind the Senator for Arizona. Yesterday Mr McCain received what could be an even more valuable vote of confidence: from the popular Governor of California, Arnold Schwarzenegger. While it would be premature even to dream of a formal alliance between the two – a foreign-born vice-president is not a variant envisaged by the Constitution – the Governor's very presence on the campaign trail is a boost to Mr McCain.

His modernity and youth-appeal would complement the Senator's age; his social liberalism would offset Mr McCain's tendency to social conservatism. On immigration and the environment, two signal post-Bush issues, the two would have no difficulty making common cause. Altogether, Mr McCain's claim to the centre ground – all-important once the nominations are decided – would be all the stronger for having the support of Mr Schwarzenegger and Mr Giuliani.

On the Democrat side, the departure of John Edwards leaves the duel between Hillary Clinton and Barack Obama pretty much where it was, but with more personal animus than before. Mr Edwards' decision to withhold his endorsement suggests he may have half an eye on the second-place slot on his party's ticket. Superficially, Mr Obama's position has been strengthened by the twin endorsements of Senator Edward Kennedy and Caroline, the daughter of JFK. Of these, the latter may be more valuable than the former. The now ageing Senator still has a following on the American left, but his support could prove a liability were Mr Obama to win the nomination and essay a move to the centre.

Even so, after she comfortably won the phantom Florida primary, it is Mrs Clinton who seems the candidate to beat. The 20-plus races next Tuesday could decide the contest in her favour, or leave it open up to the Convention. A longer contest could favour Mr Obama, while also tempting the Clintons into ugly racist innuendo of the sort the former president disgracefully drew on after Mr Obama's landslide in South Carolina.

On Tuesday, these two thrilling contests go nationwide. We hanker after a McCain-Obama match in November, but our more immediate interest – and surely that of US voters – is in any result that keeps this absorbing campaign alive.

For rolling comment on the US election visit: independent.co.uk/campaign08