After a lackluster debate, John McCain now has less than four weeks to turn the race for the White House around, as observers on Wednesday began to wonder aloud whether the Republican who once dubbed himself the comeback kid can win.

One day after McCain faced off in the second of three debates against Barack Obama, political observers said the exchange failed to up-end the front-runner status of his Democratic rival, as the contest ticks down to the 4 November vote.

"Despite John McCain's best efforts, the Arizona senator didn't knock Mr Obama from his cool evasion or even do much to rebut the Democrat's talking points," the conservative Wall Street Journal wrote the morning after the debate.

"This isn't enough to change the dynamics of the race."

Snap polls by US television networks awarded the debate — the second of a trio of presidential clashes — to Obama.

Democrats now are optimistic that — with two of three rhetorical contests over and both won by Obama according to opinion polls — the Illinois senator is an increasingly good bet to clinch the 4 November election.

'The race is over'

"The race is over," crowed Howard Wolfson, a former spokesperson for Senator Hillary Clinton, one of several Democratic rivals vanquished by Obama en route to the sealing the nomination.

Longtime Washington pundit Roger Simon pronounced neither McCain nor Obama the winner, saying that, from his vantage point, both failed in "delivering a knockout punch."

"The trouble for John McCain, however, is that he needed one," wrote Simon, a writer for The Politico daily newspaper.

The day after Tuesday's outing, Obama continued to sound an upbeat note on the stump in the midwestern state of Indiana, promising Americans "better days ahead" despite plummeting global stock markets, rising job losses and dark clouds of economic gloom.

McCain appeared at a campaign rally planned along with running mate Sarah Palin in the battleground state of Pennsylvania.

And Obama's running mate Joe Biden accused his Republican rivals of "injecting fear and loathing" into the campaign, including stoking rumors that Obama has terrorist ties.

Speaking on CBS television, Senator Biden dismissed as "malarkey" Republican allegations of unsavory ties between Obama and William Ayers, former leader of "The Weathermen," a domestic terror group. He was reacting to Palin's comments last week that Obama had been "pallin" around with terrorists."

Trailing in the polls

Trailing in most national polls, the Republican White House hopeful went to Tuesday's debate armed with an ambitious, $300-billion surprise plan to buy up the bad American mortgages that helped tip the global economy into crisis.

The gambit however failed to convince voters and the US political class that Obama is not be trusted at the helm of the state, and that McCain is in fact, the best choice to lead the country.

Political observers noted that support for the Democratic contender had been growing leading into Tuesday's face-off, and said they saw nothing in the debate that was likely to change that, including in a handful of all-important battleground states.

Meanwhile, despite the generally civil exchanges of Tuesday's encounter, observers continued to remark upon the markedly nasty tone between the two candidates.

The New York Times excoriated McCain and Governor Palin of Alaska for the tone of the Arizona senator's campaign.

"Ninety minutes of forced cordiality did not erase the dismal ugliness of his campaign in recent weeks, nor did it leave us with much hope that he would not just return to the same dismal ugliness on Wednesday," it lamented.

"We certainly expected better from Mr McCain, who once showed withering contempt for win-at-any-cost politics," it said.

McCain, widely criticised for rarely looking at Obama during their first debate two weeks ago, let his dislike of his opponent show again, when he referred to him as "that one" in a tense exchange over energy.

A CNN national poll after the debate found that 54 percent of those asked thought Obama won and 30 percent said McCain was victorious.

A CBS survey also gave the debate to Obama — 40 percent to 26 percent.

Gallup's daily tracking poll on Tuesday reflected the high stakes for McCain, giving Obama a nine point lead nationally, while the Democratic nominee is also widening his edge in key battleground states.

AFP