Imagine the scene aboard Air Force One, the US president's plane, sitting on the tarmac in Copenhagen on Friday. Barack Obama is exhausted, having flown the Atlantic overnight to back Chicago's bid for the 2016 Olympic games. He is also feeling humiliated, since his efforts on behalf of his adopted home town have been roundly spurned. Rio got the gig ? and Michelle is not best pleased.

The weary president is facing a long flight home. And he knows he is returning to a White House under siege. Healthcare, the economy, spiralling unemployment and a host of other knotty issues are blighting a first term that began with so much promise. The very last thing Obama wants to talk about is America's losing war in Afghanistan.

Enter General Stanley McChrystal, the earnest US and Nato commander in Afghanistan, clambering up the steps to Obama's cabin. The general, who has flown to Denmark after seeing Gordon Brown in London, is pressing hard for a surge of up to 40,000 extra US troops to stave off what he warns could be a strategic disaster. The calculations of Obama's advisers who arranged the meeting are more political. They know their boss has to get Afghanistan right and time is not on his side.

The result? Obama takes the meeting, as planned, and for 25 minutes he and McChrystal chew over various Afghan policy scenarios, just as they did two days before in a teleconference, and as they will do again in more meetings with senior security staff over the next two or three weeks. This root-and-branch review will determine not only the future of US military operations but those of Britain, too. It may also seal the fate of President Hamid Karzai's fraud-tainted government.

Having rushed his fences earlier this year, Obama is having serious second thoughts. With advice pouring in from all sides, the bottom-line question is: will Obama pull the plug, will he downgrade the US commitment, will he cut and run, as hawkish Republicans will interpret it? Or will he heed McChrystal and escalate, will he pursue a widening, indefinite war, will he risk a second Vietnam, as panicky Democrats see it?

Sacked diplomat Peter Galbraith's weekend broadside alleging UN complicity in electoral fraud is but the latest of many considerations pushing Obama towards some variation of the downsizing option. Karzai's manipulation of the vote had handed the Taliban its "greatest strategic victory in eight years", Galbraith said. "Obama needs a legitimate Afghan partner to make any new strategy work." In Galbraith's estimation, and that of many in an increasingly antiwar Congress, he does simply not have one.

The weekend's news that another eight US servicemen have died in Afghanistan's bloodiest year so far; polls showing plummeting public support ? only 26% believe more US troops should be deployed; and the enormous, ill-affordable financial cost of Washington's involvement are all signposts pointing to the exit. The refusal of most Nato countries to fairly share the burden, and the studied ambivalence of even ultra-loyal Britain over troop increases combine to send the president a tacit message: you are fighting a losing battle.

From George Will of the American right to Tom Friedman and Bob Herbert on the progressive and liberal left, a commentariat consensus is forming that Obama should shift to a policy of containment, using special forces, aerial strikes and money in a more closely defined campaign to disrupt al-Qaida.

Forget nation-building, they say; do not try to eradicate the Taliban, for you cannot. Instead, encourage "Afghanisation" by training the Afghan police, army and civil leaders to stand up for themselves. Learn the lessons of British and Soviet imperial history and wise up before it's too late. And it's not just commentators. This switch is forcibly urged on Obama by his vice-president, Joe Biden, and congressional Democrats.

It's unclear as yet which way Obama will jump. He may even duck and try a middle course, which would satisfy nobody. But a decisive juncture approaches inexorably. Underscoring that view, New York Times columnist Frank Rich drew a parallel with John F Kennedy's time in office. All the advice from Kennedy's military commanders and the Pentagon favoured a Vietnam escalation, Rich recalled.

"Military leaders lobbied for their new mission by planting leaks in the press. Kennedy fired back by authorising his own leaks, which, like Obama's, indicated his reservations about whether American combat forces could turn a counterinsurgency strategy into a winnable war," Rich wrote.

"Though Kennedy was outnumbered in his own White House ? and though he had once called Vietnam "the cornerstone of the free world in southeast Asia" ? he ultimately refused to authorise combat troops. He instead limited America's military role to advisory missions. That policy, set in November 1961, would only be reversed, to tragic ends, after his death."

Maybe history does repeat. For the jet-lagged, overburdened Obama, Afghanistan is looking increasingly like his Kennedy moment.