John McCain raised the spectre of a nuclear crisis if Barack Obama wins the White House, as he hammered his rival over Joe Biden’s claims that foreign enemies would test the young Democrat within six months of him taking office.

In a primetime interview with CNN’s Wolf Blitzer last night, the Republican nominee evoked memories of the Cuban Missile Crisis shortly after the election of John F. Kennedy, painting Mr Obama as “untried, untested” and a danger to national security.

“I’m astonished and amazed to hear … Senator Biden predict that the untried, untested President Obama will be tested by our enemies,” he said.

“Look, I’ve been tested. Senator Biden referred to the Cuban Missile Crisis. I was there. We came that close, as historians say, to a nuclear exchange. And Senator Biden expects...his own running mate expects Senator Obama to be tested in that way? That’s a remarkable statement, and that should concern all Americans.”

The comments capped a day on which the two opponents squared off over foreign policy experience as Mr Obama sought to play down his running mate’s remarks and Mr McCain once again stressed his military record in a bid to make up lost ground.

Mr Obama, flanked by top veteran military officials and national security advisers in the key swing state of Virginia, portrayed Mr McCain as “out of touch and running out of time,” after rejecting new Republican jibes on his national security plans.

The Democratic candidate suggested Mr Biden had only intended to say that a period of transition in the White House is always a time when foreign enemies might try to take advantage.

“Whoever is the next president is going to have to deal with a whole host of challenges internationally,” he said.

“A period of transition in a new administration is always one in which we have to be vigilant."

Though the economic crisis has dominated the pre-election agenda in recent weeks, national security looks set to re-emerge as a key issue as the campaign draws to a close. Republicans are renewing attempts to turn the key campaign issue from the economy, where voters find Mr McCain weaker, back to national security, where his credentials are more respected.

But with the US stock market continuing to dive on grim company data, sparking fears of a global recession, it is unclear whether Mr McCain’s attempt to change tack will be successful.

Mr McCain, a former prisoner of war in Vietnam, highlighted his “personal experience” in dealing with crises. He cited his role in the United States’ 1962 showdown with the Soviet Union over its missiles in Cuba. At that time, the Republican nominee was as a fighter pilot assigned Cuban targets.

“I know how close we came to a nuclear war and I will not be a president who needs to be tested. I have been tested,” he told an enthusiastic rally on a high school football field in Green, Ohio, another key battleground.

Just 13 days before the presidential election, Mr McCain warned the Democratic Illinois senator not to take victory for granted, despite his mammoth financial edge and solid lead in a slew of opinion polls.

“My opponent’s looking pretty confident these days,” he said in New Hampshire, a state which revived his moribund presidential campaign earlier this year.

“He’ll be addressing the nation soon. He’s got another one of those big-stadium spectacles in the works, acting like the election is over."

A Fox News survey and a Gallup Daily survey each put Mr Obama up nine points, while the Rasmussen daily tracking poll had him ahead by 51 per cent to 45 per cent.

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