Leading article: A US election that has turned the world on to politics

One of the longest and most enthralling US election campaigns in memory will reach its climax four weeks tomorrow, when Americans finally cast their vote. But it is salutary to consider how completely the political landscape has changed from 18 months ago when the bare outlines of the contest were being established and Hillary Clinton's nomination seemed a foregone conclusion for the Democrats.

Then, the topic central to the electoral agenda was the war in Iraq and US engagement overseas. For the first time, perhaps since the Vietnam war, a President's failed foreign policy looked set to dominate the campaign. That is no longer so. Iraq did play a role; it raised the profile and strengthened the claim of Barack Obama, whose anti-war stance distinguished him from the other candidates and specifically from Mrs Clinton. It may be part of the reason why he prevailed. But the focus is now on the financial crisis gripping the Western world and its origins in the United States. Both Mr Obama and the Republican nominee, John McCain, have had to add new breadth and new seriousness to their campaigns.

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This is still an election of firsts. Mr Obama is the first black American to win the nomination for a major party, and he has done so, admirably, in eschewing the race card. His rhetorical brilliance has galvanised the country and drawn a new generation of Americans – and not just Americans – into politics. The excitement generated by his campaign has resonated abroad, including in Britain, where more young ethnic minority candidates are finding themselves similarly engaged. Whatever the result, what might be called the Obama effect has been impressive.

If Mr Obama is one of the youngest and least experienced candidates to run for the presidency, his opponent is one of the oldest. Thus far, though, age has made as few overt appearances as race. The issues, it seems, have been just too big for voters to worry about how many years' of experience the next President has under his belt. Refreshingly, the sole consideration has been how well he will be able to do the job.

Beyond balancing the ticket, a candidate's choice of running mate has tended to be a temporary distraction with little real impact on the outcome. Mr McCain's nomination of Sarah Palin has, at least temporarily, changed that assumption. The first woman to feature on a Republican presidential ticket, the first-term governor of Alaska seemed a gamble that jeopardised Mr McCain's trump card of experience.

But Mrs Palin has undoubtedly brought something to the ticket, too: a plain-speaking, often folksy, heartland appeal that exemplifies a different type of politics. She carried off her convention speech triumphantly, and navigated her debate with the veteran Senator, Joe Biden, without mishap. For many Europeans, she may seem an alien species, but she appeals to a strand of American populism that the other three candidates have often failed to reach. If not in 2008, she may have a future in 2012.

After months in which the two nominees have run neck and neck, the economic crisis seems now to be benefiting Mr Obama. With even President Bush accepting that the state must play a role at such a time – and accused of embracing socialism for his trouble – the Democrats are starting to look as though this year they might be on the right side of history. It is an impression reinforced by the first hint that the McCain-Palin team has decided to "go negative": Mrs Palin's claim that Mr Obama has associated with terrorism – a charge relating to a group active when the candidate was still a child.

It would be regrettable if such an exhilarating race were to end on a note of sourness. The gravity of the economic situation and the proven impotence of the outgoing President give Senators McCain and Obama abundant material for serious campaigning. As we watch from the sidelines, this is what we would ask for.