HEADING INTO the New Hampshire primary on Tuesday, the US presidential election has eight credible candidates still standing, but one dominant theme. Change is written on every Democrat placard, and is the focus of every speech that Barack Obama, Hillary Clinton and John Edwards make. More surprisingly, it is also the keynote for all of the Republican front-runners. For the first time in more then 50 years, there is no incumbent president or vice-president running for office, but few could have predicted such an across-the-board disavowal of the establishment.

Mitt Romney's stump speech asserts that America has been let down by "Washington insiders", in a veiled jab at John McCain, who portrays himself as a tireless campaigner against greed and hypocrisy in Congress. Mike Huckabee, seeking to broaden his base beyond the evangelicals who swept him to victory in Iowa, tells conservatives that "what we're seeing is that this campaign is not just about people who have religious fervour. It's about people who love America, but want it to be better and believe that change is necessary and it's not going to happen from within Washington."

In their victory speeches in Iowa on Thursday night, Obama and Huckabee employed similar rhetoric, presenting themselves as unifiers capable of healing the vicious party political schisms that have characterised this divided "do-nothing Congress".

"You said the time has come to move beyond the bitterness and pettiness and anger that's consumed Washington," Obama told his jubilant supporters. "To build a coalition for change that stretches through red states and blue states. Because that's how we'll win in November, and that's how we'll finally meet the challenges that we face as a nation."

Huckabee, for his part, spoke of his desire "to make Americans, once again, more proud to be Americans than just to be Democrats or Republicans. To be more concerned about going up instead of just going to the left or to the right." Even Clinton, in defeat, was singing from the same hymn sheet. "I congratulate Senator Obama and Senator Edwards," she conceded, "together we have presented the case for change."

Democratic pollster Peter Hart and Republican pollster Bill McInturff recently asked voters whether they felt change was necessary: 24% of respondents said America should maintain a steady course, with minor adjustments; 29% said the country needed to turn the page and pursue significantly different policies; and 46% replied that major reforms and "a brand new and different approach" were required.

New Hampshire presents a very different challenge to Iowa. Its residents like to boast of their decisive role in American politics. Former governor John Sununu declared in 1988 that "the people of Iowa pick corn, the people of New Hampshire pick presidents". The "Granite State" has a reputation for relishing the opportunity to puncture bubbles inflated in Iowa.

Like Iowa, it is overwhelmingly white, but wealthier, and more concerned with tax issues and national security than agriculture. Other than Alaska, it is the only state in the US with neither a sales tax nor an income tax. New Hampshire's official motto is "live free or die". This pronounced libertarian streak and suspicion of big government could make Republican maverick Ron Paul a factor, despite his poor showing at the caucus.

More than 40% of New Hampshire's voters classify themselves as independent, meaning they are free to participate in either the Democrat or the Republican primary on Tuesday. This creates an intriguing tussle for votes between Obama and McCain, the two candidates with most appeal to independents, based on the results in Iowa and McCain's past record in New Hampshire.

Last week, a Times/Bloomberg poll found that 61% of New Hampshire's independents planned to vote in the Democratic primary, against 39% in the GOP (Grand Old Party) contest. And among those who had already decided whom to support, more than twice as many said they would back Obama, compared with McCain. The wave of optimism and media attention that greeted Obama's win in Iowa must hurt McCain's New Hampshire chances, but it is still his best chance to reassert himself as a potential nominee. In 2000, he beat George Bush by a huge margin - 19% of the total vote - and even a slim victory this time would set him up as a serious contender once again.

In 2006, Democrats captured both houses of the New Hampshire legislature for the first time in 132 years, ousting two incumbent Republican members of Congress from office. On issues, the Times/Bloomberg poll found New Hampshire's independents tended to agree with Democrats more than with Republicans, naming Iraq, the economy and healthcare as their top priorities. Illegal immigration, the subject which has dominated almost every Republican debate, was a distant fifth, behind national security.

New Hampshire remains a critical test, but its role has changed, thanks to the extraordinary compression of the primary season, as states hold their contests earlier in the scramble for influence. There are only 22 delegates at stake, compared with 128 in Michigan, 185 in Florida and 370 in California, so just like in Iowa, it is all about perception and momentum.

Super Tuesday, the first nationwide assessment of electability, used to be the second Tuesday in March. This year, it is the first Tuesday in February. Twenty-four states, including such populous, delegate-heavy states as New York and California, are holding their primaries on the same day, creating the need for a new name, although nobody can quite agree what it is: Super Duper Tuesday, Supernova Tuesday, Giga Tuesday, Tsunami Tuesday.

ON the Democrat side, there are two major questions heading into New Hampshire: can Hillary Clinton successfully portray herself as a "comeback kid" by using the example of her husband's revival in the 1992 election? And is John Edwards finished?

Clinton will be well aware that only two Democratic candidates since 1976 have won both early contests, and neither Al Gore nor John Kerry went on to become president. Robert Zimmerman, one of her most vocal supporters in the Democratic National Committee, argued that losing Iowa could even be a positive: "Being the underdog will be very liberating".

The strategy favoured by Clinton's chief adviser, Mark Penn, stressing experience over change as a theme, has been all but abandoned, replaced by a more nuanced message about the ability to effect the change everybody wants. Her challenge now is to attack Obama directly on his record, without coming across as small or mean. On Friday, Bill Clinton admitted that "I just wish we had 10 days instead of five" to bounce back.

At her first rally in New Hampshire, Clinton observed that "anyone we nominate will be thrown into that blazing inferno of a general election. I've been through the fires, and it makes it far less likely they are going to be able to do to me what they intend to do to whomever we nominate. Who will be able to stand up to the Republican attack machine?"

Her new pitch takes aim at Obama's signature rhetoric, declaring that what America needs is someone who can "actually deliver change", not "false hopes", but there is still a reluctance to get too personal when negative campaigning has so far proved to be a turn-off with voters on both sides of the political divide.

In any case, how to attack Obama? His early opposition to the Iraq war provides him with an enormous advantage on what is still the number one issue for Democrats. His positions on healthcare and the economy are broadly similar to Clinton's, forcing her to niggle at the details, rather than the broad sweep of policy. Her campaign has highlighted Obama's liberal voting record, suggesting he would be soft on crime and an easy target for Republicans because he once opposed mandatory minimum sentences for federal crimes.

"On a lot of these issues it is hard to know where he stands, and people need to ask that," she told a crowd in Manchester, New Hampshire, but that was as pointed as it got.

Amid the euphoria that surrounded Obama's victory in Iowa, it was easy to lose sight of the national polls that still show Clinton way out in front. Taking the average of the five most recent surveys, she leads Obama 34% to 27% in New Hampshire, 45% to 22% in Michigan, 41% to 21% in Nevada, 43% to 24% in California. These were all pre-Iowa polls, of course, but they show that it takes some chutzpah for Clinton to suddenly present herself as an outsider. She still heads an unrivalled political machine, and whatever happens in New Hampshire she will be a formidable opponent on Super Tuesday and beyond.

Clinton's perception problem was nicely articulated on Iowa caucus night by NBC anchor Tim Russert: "The Clintons are professionals. And the one message tonight may be that people don't like professionals. They may be saying to the slick crowd no mas' no more."

Edwards, for his part, is retuning his populist message for a new demographic, aware that he faces a tougher test in New Hampshire, which has far fewer blue-collar workers than Iowa. Many commentators have suggested that in failing to win Iowa, where he had concentrated so much time and so many of his meagre resources, the senator from North Carolina has already missed his best chance to make an impact in the race.

New Hampshire is historically inhospitable to Southern candidates and dealt a major blow to his chances in the 2004 primaries. Few expect the result to be any different this time, and if he finishes third, as predicted by most analysts and all the most recent polls, his candidacy will struggle to survive.

The Republican field, by contrast, is more congested than ever. Huckabee's victory in Iowa sets up a three-way struggle between McCain, Romney and Rudy Giuliani to be the Wall Street and national security candidate. Whoever emerges on top will then have to take on Huckabee, who leads a populist evangelical insurgency within the party. More than six in 10 of the Republican caucus-goers in Iowa were born-again Christians who voted overwhelmingly in Huckabee's favour. In secular New Hampshire, he cannot hope for a repeat, but will move on to South Carolina and Florida, in particular, confident of a strong showing.

McCAIN goes into New Hampshire as favourite. A summer crisis in his campaign funding forced him to all but camp out in the state, relying on a healthy win there to reignite his campaign. In his fight against Mitt Romney, the most negative and nasty of the election sub-plots, McCain has the backing of the state's most influential local newspapers and a five-point lead in the week before the primary. A McCain win would leave Romney facing a last stand in Michigan, the state where he grew up.

The Republican establishment views Huckabee as a dangerous wildcard, not least because he has characterised party grandees as a "wholly owned subsidiary of Wall Street". His appeal to evangelicals threatens to split the party in half, with small-government, low-tax conservatives on one side and evangelicals on the other. For as long as Romney and McCain divide the party faithful's vote, he will remain a credible candidate.

As Huffington Post columnist Thomas B Edsall observed on Friday: "An extended fight pitting Huckabee against another leading Republican candidate would very likely leave the GOP with scars difficult to heal by November 2008".

The record turnout in Iowa, allied to polls suggesting that almost two-thirds of New Hampshire's independents intend to vote in the Democratic primary, provides Clinton and Obama's party with great reason to hope, whoever wins the nomination. But as Edwards noted in his post-caucus speech on Thursday night, so far only the theme of the election has been settled: "One thing is clear tonight. The status quo lost. Change won."