When confronted with a rash of new polls showing that the economic crisis has propelled Barack Obama farther ahead in the race for the White House, John McCain gave a shrug yesterday and offered this explanation: "Because life isn't fair."

Then he laughed.

The Republican nominee has not always been so apparently relaxed and even-tempered in recent days. On Wednesday night, when Mr Obama went over to greet him on the Senate floor before they voted on the bailout Bill, Mr McCain could barely look at his rival as they shook hands for less than a second.

Earlier this week he became irritable, even angry, when responding to questions from the Des Moines Register in Iowa - one of a number of formerly Republican states where Mr Obama now has a lengthening lead.

Asked about a growing chorus of conservative criticism directed at his running-mate, Sarah Palin, he replied with withering sarcasm. "Really?" he said, "I haven't detected that, haven't detected that in the polls, haven't detected that among the base."

He went on to suggest that attacks on his vice-presidential nominee came from the Washington insider elite - a "Georgetown cocktail party person who calls himself a conservative and doesn't like Palin" - adding, with a final dose of scorn, that he wished them "good luck".

Luck is a commodity that Mr McCain needs more than anything else right now. His strategists have long since recognised that this seems to be a Democratic year and, on a level playing field, Mr Obama is likely to win the White House. Their response has been to churn up the turf with every tool at their disposal.

The attacks on Mr Obama as a vacuous celebrity, the choice of the untested Mrs Palin or the decision to suspend his campaign temporarily because of the financial crisis, have all been high-risk manoeuvres bordering on the reckless.

While they succeeded to varying degrees in the short term by snatching the spotlight away from the Democratic nominee, they have also undermined his brand as a sober, experienced statesman who puts country first and would rise above the partisan bear-pit of American politics.

Episodes such as that in Des Moines this week have also led to questions about his temperament, with Democrats wasting little opportunity to imply he is an angry, erratic old man.

An election that Republicans had hoped to turn into a "referendum on Barack Obama" has become a verdict on Mr McCain's own judgment and the credentials of Mrs Palin. Polls from the battleground states where this election will be decided suggest that Mr Obama's calm and cautious front-running strategy is grinding forward.

He has clear leads in target states like Florida and Virginia, while also leaping ahead in states such as Minnesota, Michigan and Pennsylvania, which the Democrats won four years ago but had, until this week, been in the toss-up category. Yesterday Mr McCain's campaign was reported to be pulling out of Michigan.

His campaign is now at a crossroads. Mike Murphy, who ran his last bid for the White House eight years ago, described how many established Republicans had become exasperated with recent decisions. "Almost to a person they are dismayed by what they see as the stunning lack of competence in the McCain operation," he said.

Others believe that he will roll the dice again and become even more aggressive, arguing that Mr McCain should start attacking Mr Obama over his Chicago past, including the controversial pastor Jeremiah Wright, the convicted fraudster Tony Rezko and the 60s radical Bill Ayers.

Mr McCain insists that he remains undaunted by the odds against him. He dismissed recent surveys as "temporary", adding: "I understand there are going to be ups and downs in campaigns. I'm happy where I am. I'm the underdog. I love being the underdog."

The Republican likes a gamble. When asked which team he fancied for the baseball play-offs, he pointed out the LA Dodgers as one that "could surprise everybody". He added: "But that shows you why I am not a rich man."