The emphasis at the Democratic Party convention in Denver on 25-28 August 2008 is set to climax with a speech from the party's presidential nominee Barack Obama that seeks to project the candidate as never before to the national electorate. The full impact of the convention and its closing address on what has become an increasingly even race is is yet to measured, but its unifying momentum - symbolised by the high-profile endorsements of Obama by Hillary Clinton and (more strikingly) Bill Clinton - was intended to allow the party to put the bitter divisions of the primary race behind it and march forward at last to meet John McCain, the Republican candidate, in a fair and equal fight.

Now it's the turn of the Republican Party, in its own convention in Minneapolis-St Paul on 1-4 September. After that, the two-month countdown to the end of an extraordinary election campaign will have begun. On 4 November 2008, the American people will elect a new president, and the whole world will be watching.

But the world is not waiting for the result. It is crowding in on the campaign already. A succession of global crises have already made it certain that the final lap of the presidential race will be concerned above all with foreign policy - possibly with huge implications for the eventual result.

A crowding planet

Two events in August 2008 in particular - Russia's ruthless incursion into Georgia and the enforced resignation of Pervez Musharraf in Pakistan - underline the collapse of the George W Bush administration's foreign policy, and together guarantee that the last phase of the election campaign will largely be dominated by foreign affairs. That is a field in which John McCain thinks he has a commanding advantage over Barack Obama, who will have to play his cards with great skill to prove his rival wrong.

This is precisely why the Illinois senator has chosen Joseph Biden, chairman of the senate foreign-relations committee and an expert on foreign policy, as his vice-presidential running-mate. The Democrats are already claiming that Biden - who also made a characteristically forceful speech at the Denver convention - will enable Obama to laugh off Republican claims that he is too inexperienced in foreign affairs to be president.

It may be so. Biden is undeniably a veteran of the international circuit, known and liked by the powerful and influential all over the world. It is even argued in favour of the Obama-Biden ticket that the whole character of the vice-presidency has changed as a result of the way that the hawkish Dick Cheney has reinterpreted its role: the suggestion is that Biden would be able to function almost as a foreign-policy assistant-president, and that this could function in the campaign to neutralise the nervousness among voters about Obama's fitness for the White House.

If that is the Obama team's calculation, it is unrealistic. However wise and experienced his vice-president may be, a president will always be on his own when it comes to making hard decisions.

Also in openDemocracy on the United States election:

openUSA is a new part of the openDemocracy network, publishing daily commentary and analysis of the 2008 election - both from the United States itself and around the world - and links to the best campaign coverage.

This week: Solana Larsen blogs from the Denver convention.

To access openUSA, click here.

However, the Democrats' foreign-policy team was a strong one even before Joe Biden came on board. It can count on the advice of Richard Holbrooke, a man of great force and experience who is likely to be secretary of state in the event of an Obama victory; of Holbrooke's rival for that job, a former national-security adviser under Bill Clinton, Anthony Lake; former secretary of state under Clinton, Madeleine Albright; Jimmy Carter's national-security adviser Zbigniew Brzezinski; and of course Bill Clinton himself.

The advice will be needed - for it is certain that this will be a foreign-policy election. To be sure, the problems of the economy - from high gasoline and energy prices, job losses to the collapse of the housing market - will be much on voters' minds. But these too are deeply linked to its policies overseas, which in both economic and political terms have left the Bush administration's reputation in tatters.

As the election nears, it will not be possible to ignore the fact that wherever America looks - whether it is Israel and Palestine; Iraq, and much of the middle east; Russia and its "near abroad", from Georgia to Ukraine; Afghanistan and Pakistan; a resurgent China; Latin America, with its new generation of leaders; a Europe in disillusion - its leaders for the past eight years have brought it to a desperate low in influence. After years in which the public in the United States took it for granted that their country was "the lone superpower", almost everywhere its power is challenged.

A twin crisis

This uncomfortable reality has been highlighted above all by the Georgia-Russia war and the Pakistani imbroglio. In the United States, events in Georgia have been framed in stark moral terms: brave little Georgia as a pure maiden ravaged by the Russian bear. Yet, at least in the short term, Russia's heavy-handed response to Georgia's attack on South Ossetia can be interpreted in another way: as evidence that the lone superpower has lost its teeth.

President Bush has strongly advocated Georgian and Ukrainian membership of Nato. Yet the Pentagon has admitted that it cannot challenge the Russian army in Georgia; while any American intervention in Ukraine (where Russians who constitute almost a quarter of the country's 46 million inhabitants) would be seen by Moscow as even more grave a threat as the missile-defence installations agreed with Poland.

Washington's basing of anti-ballistic missiles in Poland - ostensibly intended to deter Iranian missiles, which do not yet exist - was accelerated by Russia's incursion into Georgia. American Patriot missiles, with American crews, have been moved ostentatiously to Poland from Germany. In response to Russia's continued presence in parts of Georgia, American warships have now entered the Black Sea.

The former Warsaw Pact and Soviet republics share Washington's anger at Russian behaviour. But they have been disillusioned by the weakness of the American response. They saw Nato membership as a guarantee of protection against reviving Russian nationalism. The Georgia incident is causing anguished reflection about what and who they can count on if they were to be threatened by Russia.

Godfrey Hodgson was director of the Reuters' Foundation Programme at Oxford University, and before that the Observer's correspondent in the United States and foreign editor of the Independent. He reported the presidential elections of 1964, 1968, 1972, and 1976 for various British and American media, and was co-author (with Lewis Chester and Bruce Page) of the best-selling account of the 1968 campaign, An American Melodrama (Viking Press, 1969).

Among his other books are: The World Turned Right Side Up: a history of the conservative ascendancy in America (Houghton Mifflin, 1996); The Gentleman from New York: Senator Daniel Patrick Moynihan (Houghton Mifflin, 2000); More Equal Than Others: America from Nixon to the New Century (Princeton University Press, 2006); A Great and Godly Adventure: The Pilgrims and the Myth of the First Thanksgiving (PublicAffiars, 2007).

Among Godfrey Hodgson's recent openDemocracy articles on American politics:

"The United States election: time for ‘change'" (10 January 2008),

"America's change election: reality or mirage?" (11 February 2008),

"‘Superdelegates' and the US election" (25 February 2008),

"The lost election year" (15 May 2008),

"Barack Obama: at the crossroads of victory" (11 June 2008),

"A game of two halves" (15 July 2008),

"Barack Obama's political tour" (28 July 2008),

"Welcome to the party: American convention follies" (18 August 2008).

The blow to American power in Pakistan is arguably even more damaging than in the "ex-Soviet space". President Bush had chosen the authoritarian general-president Pervez Musharraf as his ally in Pakistan, and called him a champion of democracy - even when, to the great majority of Pakistanis, it was the opposition to Musharraf that represented a democratic challenge to dictatorial rule. The evidence of his violations of rights over a decade of rule makes a mockery of the administration's claims (see Shaun Gregory, "Pakistan's political turmoil - Musharraf and beyond", 27 August 2008).

Pakistan is facing accumulating security and political crises. Yet before and after Musharraf's fall, its people bitterly resent American criticism of its forces' failure to uproot the Taliban from the unruly "tribal areas" in Swat and Waziristan which the Afghan Taliban treat as a safe haven, and where Osama bin Laden and the other leaders of al-Qaida are thought to be in hiding.

Inside Afghanistan itself, western efforts to stamp out the Taliban are also failing as the militias creep closer to Kabul. The opium-crop on which much of the Taliban's income depends is bigger than ever. The continued casualties from American air-strikes - one of which, on 22 August, killed ninety civilians in a district of Herat province- guarantee even more sympathy (and perhaps recruits) for the movement (see Paul Rogers, "Afghanistan: on the cliff-edge", 28 August 2008).

Washington therefore now faces a painful dilemma. It must either give up the "war on terror" in the Afghan/Pakistan theatre; or it must intervene directly inside Pakistan, thus infuriating the majority in a country of 160 million, armed with nuclear weapons.

A month of surprises

It is here that the ruins of the George W Bush administration's foreign policy impinge directly on the presidential election. Barack Obama owes much of his passionate support to the fact that he opposed the Iraq war from the beginning. (Joe Biden may have opposed the war, but - like Hillary Clinton - he voted for the resolution that permitted it.) Obama knows that he is vulnerable to charges of callowness in national-security questions. John McCain, a national war-hero and a long-serving member of the senate armed-services committee, is only too keen to highlight Obama's alleged weakness in this field.

Obama's week-long trip to Iraq, Afghanistan and Europe on 19-26 July did not wholly succeed in erasing doubts about his competence in foreign policy; his week-long holiday in Hawaii turned out to coincide with start of the Georgia-Russia conflict, and his response in any case did him little good. The Republicans are hammering away at the issue. The worry for Obama is that he has begun to fall behind McCain in two polls published on 20 August (Reuters/Zogby) and 26 August (Gallup). More generally, the two parties are now running almost neck-and-neck. What seemed at one time to be becoming almost a smooth walk to the summit of power is turning into a bitterly fought, close race.

Pakistan-Afghanistan and Russia-Georgia are areas where Obama must not appear weak. The Democrats, after all, have long - at least since the Vietnam war - had the reputation of being weak on national security. If Obama's poll position slides, and if John McCain maintains a foreign-policy stance virtually indistinguishable from that of George W Bush and Dick Cheney, then the pressure on Obama to compete with McCain's militancy could become irresistible.

Many experienced old political reporters (here I plead guilty on both counts) always look out for an "October surprise" in the closing weeks of an American presidential-election campaign. This year the October surprise seems to have come in August - which is not to say that there will not be another in October.

It may also be in another part of the landscape of challenges the United States is facing: Iran (see Paul Rogers, "Iran and the American election", 5 June 2008). The Bush administration suspects Mahmoud Ahmedinejad's regime of using a civil-nuclear programme as a covert attempt to build nuclear weapons, The diplomatic efforts of western European states to persuade Iran to give up its uranium-enrichment programme have not been successful. The Georgia events may make the Europeans less keen to follow Washington's lead. There is an outside chance that the United States might be tempted to bomb Iran's nuclear plants. There is a larger possibility that Israel might do that very thing. What would Barack Obama say?

A change in the weather

The American military is reported to believe that Iran's nuclear plants are too many and too deeply implanted in hardened underground sites to be destroyed. But the Bush administration shows every sign of wanting to defend its reputation for forceful action. Israel has shown even clearer signs of contemplating action against Iran of the kind it undertook against Saddam Hussein's Iraq in 1981 (when, admittedly in very different circumstances) it bombed the nuclear facility at Osirak. It may be a sign of what is to come that the Israel Defence Forces (IDF) staged an elaborate operation over the eastern Mediterranean on 2 June 2008 to demonstrate, or perhaps to perfect, its capabilities in coordinating a bombing attack against distant and multiple targets (see Paul Rogers, "Iran, Israel and the risk of war", 24 July 2008).

If relations with Iran were to escalate into a crisis - and if either the United States or Israel bomb Iran in an "October surprise" - the repercussions on the presidential election would be explosive. Many Americans might then feel more comfortable with a naval officer in the White House than with a former community worker - whose great assets, moreover, might (if in principle attractive at a time when America was in a hopeful and generous mood) be depicted as inappropriate when it faced yet more conflict with yet more enemies.

In those circumstances - and even in existing ones - foreign policy could lose Barack Obama the election. If it does not, and he wins decisively or by a whisker on 4 November, it might transform the whole tone of his administration - as the Bay of Pigs invasion stripped the John F Kennedy administration of a certain aura.

Obama has presented himself as, above all, the candidate of "change". But as Russia throws its weight around on its periphery, as Pakistan implodes, and as American forces are put under severe pressure in Afghanistan and Iraq, the impact on the election could yet be decisive. In such circumstances, neither American voters nor the American media are going to be in a mood for sweetness and light in the White House. Even if he gets there, the kind of change Barack Obama represents would find a world that is souring and darkening for America a tougher nut to crack.