Why is it so close? That’s been the chatter after these past two weeks in the three-month run of the Obama-McCain smackdown. The Obamaphiles are nervous that their man has stalled in the polls after what, objectively, was a successful trip overseas. The McCainites, terrified of a Democratic wave, are taking solace in the failure of Barack Obama to break away. The straggling Clintonites are busy preparing their told-you-sos.

There are any number of theories offered for the tightness. One is that Obama is too temperamentally aloof for most Americans. According to the columnist Maureen Dowd, he is the Mr Darcy of American politics, too proud, while Americans are still a little too prejudiced. Or maybe Obama is too popular with Germans for his own domestic good (he’s lucky he didn’t hold a rally on the Champs Elysées). Or is his orthodox liberalism in many areas seeping through, while America remains a centre-right country? Others posit that the only halfway normal Americans who focus on the campaign in early August are the elderly, and they are demographically more in tune with John McCain.

Who knows for sure? My view is that McCain was always the most appealing Republican in the current atmosphere and Obama is, for many people, a less well-known and riskier bet. But two factors are undervalued. The first is Iraq. It’s easily forgotten but Obama’s candidacy would never have gained the slightest traction were it not for his opposition to the war from the start. It’s what distinguished him from Hillary Clinton and, in the midst of apparent chaos and drift in Mesopotamia, his campaign gave voice to those who simply wanted to cut American losses and move on.

However, there’s a difference between Iraq in mid2006 and Iraq in mid2008. The swift decline in violence and the growing confidence of the government of Nouri al-Maliki have changed the debate from how to leave as quickly as feasible to the costs and benefits of staying longer or leaving sooner, and the tactics of each option. The catastrophe endures, of course; the political progress in Baghdad remains fitful, as the Iraqis’ failure last week to compromise on plans for provincial elections this autumn demonstrates; and the financial costs grow all the time. However, the sharp decline in American deaths has rescued the neo-imperial project from universal obloquy. McCain can rightly claim that he was more right about General David Petraeus’s tactical shift than Obama was. In some respects, he was more right than even Petraeus was.

To be sure, Maliki’s endorsement of Obama’s withdrawal timetable was a big blow to the McCain effort to describe the Democrat’s policy as surrender or betrayal. However, any news that takes the edge off Iraq as a total fiasco helps the Republican. Americans don’t like to admit defeat and the face-saving qualities of the surge give McCain an opening to end the war with less disgrace than might have been the case. McCain’s position, after all, was to hang in while Iraq burnt because the alternative was worse. His new position is to hang in and somehow turn a strategic blunder into a strategic success. This is a much, much better place for McCain to be than he was just five months ago. Still not great; but no longer awful.

The second factor, I’d argue, is, paradoxically, Democratic strength. The shift away from the Republicans is pronounced everywhere and few doubt that the Democrats could make big gains in both House and Senate this autumn. This is partly behind the worries about Obama: he’s trailing his party by a significant margin. However, it may be that the margin is precisely what’s giving voters pause. The threat of the kind of Republican agenda that propelled George Bush from 2002 to 2006 is, after all, much diminished. McCain, moreover, is not so bad a figure to deal with a Democratic Congress from the perspective of many independent voters, especially since Congress is pretty much reviled as well.

The choice has evolved to that between an all-Democratic government, headed by a senator whose newness is still one of the most striking things about him, and an old, familiar warhorse who irritated all the right Republicans at one point or another and has a record of bipartisan achievement. Seen in that light, the voters’ reluctance to swing behind Obama in landslide numbers is understandable.

Obama has huge liabilities. He has never held real executive office and has been in Washington barely for a single senatorial term. He came out of nowhere to dominate the scene in ways that many Americans are still trying to process. He has been criticised as a far-left extremist, a prissy elitist, a cynical centrist and a secretly Muslim fraud. Examining this figure who is asking to be president at the tender age of 47, watching him adapt and move on the national state, is a sensible precaution. Americans are a prudently cautious lot and it speaks well of them that many are reserving final judgment.

And, as we learnt all too brutally in 2000, the US election is decided by the electoral college, not the national vote. There, a small advantage can translate into big wins, as the system is first past the post. Obama is now ahead by only two points or so in several key states: Colorado, Michigan, Ohio and Virginia. If he were merely to maintain his lead, he would snag 322 electoral votes to McCain’s 216. That’s a bigger victory than anyone since Bill Clinton’s second term and bigger than Jimmy Carter’s victory in 1976.

Put like that, and considering the racial Rubicon that Obama is hoping to cross, perhaps what’s striking is that a young black liberal Democrat is still the clear favourite. Nationally, McCain has yet to get much more than 44% of the vote, while Obama hasn’t sunk below 46% since May. Moreover, McCain has never led Obama in two months of a national match-up. That’s why it’s still Obama’s to lose. There will be some swings ahead, if the past is any guide, but so far the basic dynamic hasn’t really changed. And it’s McCain who has to change it. And soon.

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