Leading article: A presidential succession decided by recession

But race lurks as an unknown quantity for Barack Obama

The televised debates are over, the final countdown has begun, and – though it may seem a bold statement to risk after such a roller-coaster campaign – the US presidency now looks very much like Barack Obama's to lose. Wednesday night's debate was the last chance for John McCain to score a knockout blow in front of a television audience of millions. He did not disgrace himself – far from it – but he did not land that final punch.

The Republican nominee successfully distinguished himself from George W Bush and his chequered presidency. And he came across as a determined fighter, standing up for ordinary Americans. His tale of "Joe the Plumber", who feared his livelihood would be threatened by Mr Obama's tax plans, became the pivot for the whole debate. But it was not decisive. Mr Obama kept his cool; he was incisive and well-briefed.

Few can now argue that the Democrat's relative youth and inexperience in national politics are electoral liabilities – almost the reverse. As Mr Obama gained in political stature, the three debates seemed to point out Mr McCain's advancing age. Even the second, town hall meeting-style encounter, in which he was supposed to excel, showed him as much bumbling as connecting. Age has not (yet) been a real factor in this campaign, perhaps because it threatened to be a drawback for both. Now that Mr McCain is looking all his three score years and 12, there may be no need for Mr Obama to mention it. Every appearance drives the message home.

Most of all, though, Mr Obama appears to have benefited from the financial crisis, which has given new pertinence to his campaign's theme of change. After months in which he seemed to be making less headway than any Democratic nominee was entitled to expect, given a tired, two-term Republican administration weighed down by two wars, his lead has recently solidified. The sharp deterioration in the US economy is surely one factor: it has reminded many Americans of why government might not be such a bad thing after all, and exposed the downside of the Bush administration's faith in the free market.

But Mr Obama has also been equal to the opportunity. His energetic and generally well-informed response to the crisis has contrasted with Mr McCain's often hazy grasp of essentials. Economics was never Mr McCain's strong suit. And while his gift for empathy can compensate to a degree, it has looked increasingly insubstantial as the crisis has sharpened. His introduction into Wednesday's debate of Joe the Plumber was a good try and an unconcealed pitch for the votes of modest but aspirational Americans, who are often swing voters: the so-called Reagan Democrats and their equivalents. But it was probably not enough. If the polls are to be believed, it is these voters whom Mr Obama is increasingly winning over.

The polls, however, must be treated with more caution this year than in almost any presidential contest before. As the first non-white candidate to be nominated by a major party, Mr Obama would make history if he won. But his race is a completely unknown electoral quantity. Many suspect that voters are concealing the extent to which race will inform their choice.

The way the polls have moved in recent weeks, however, suggests that – as in 1992, when the governor of a small southern state beat the incumbent – the perception of economic competence could trump all else. This year, with race in the frame, such a prospect would be even more heartening than it was then.