Crunch time for Mitt Romney

When nervous Republican donors expressed fears to Mitt Romney's advisers about his campaign this summer, they were reassured that there were three key "impact" moments ahead that would change the White House race.

The first two - the choice of a vice-presidential candidate and the party convention in Tampa - have come and gone without delivering the bump in support that Romney desperately needed.

With President Barack Obama holding his lead in the polls, that leaves just the final play in that Romney game plan: the three presidential debates.

When the two men walk onto a stage in Denver this week in front of a national television audience expected to exceed 60?million, the stakes could not be higher for the Republican side.

In the words of Newt Gingrich, the former Republican presidential candidate, the 90-minute showdown on Wednesday will be "the most important single event in Mitt Romney's political career".

After weeks of campaign missteps, the former Massachusetts governor is desperate to put the focus back on the country's anaemic economic recovery, for which he was handed ammunition last week by statistics showing American economic growth was even slower than expected.

But the pressure is high for him to land some heavy blows, if not a killer punch.

He has been working for months on his debate preparations at his mansion in New Hampshire, often in hotel rooms during campaign stops and most intensively for three days recently at a friend's home in rural Vermont.

In these mock debates, the role of Mr Obama has been played by Rob Portman, the Ohio senator, a familiar face in Romney's entourage.

He also honed his debating skills during the long onstage encounters with party rivals during the primary battle.

The two camps keep details of their preparations under careful wraps. But Romney has already indicated one line of attack: to portray Obama as a serial distorter.

"I think he's going to say a lot of things that aren't accurate," he said, when asked what he had learnt about Obama as a debater. "I'd be tempted to go back to that wonderful line by Ronald Reagan - 'There you go again'," he added, referring to a withering put-down by the then Republican candidate when President Jimmy Carter attacked him in a 1980 debate.

The tactic was endorsed by Karl Rove, who helped George W Bush prepare for the debates of 2000 and 2004.

"Romney must call out the president," he advised. "That is not so easy. Romney can't call Obama a liar; that's too harsh a word that would backfire.

"Romney must instead set the record straight in a presidential tone - firm, respectful, but not deferential. And a dash of humour is worth its weight in gold. He should deal comprehensively with several of Obama's untruths and, having done so, dismiss the rest as more of the same."

It is a sign of the challenge facing Romney, a candidate often criticised as wooden and with a recent track record of verbal gaffes, that his last great chance for a breakthrough is to out-debate a president who is himself renowned for his oratory.

But the debate format does not particularly suit the president either. He has a tendency to come across as professorial and condescending. And given Obama's lead in the polls, the debate is essentially his to lose.

As the clock counts down to Wednesday evening, both camps are trying to lower expectations.

The Romney side sought to portray their candidate as the underdog.

"President Obama is a uniquely gifted speaker, and is widely regarded as one of the most talented political communicators in modern history," wrote Romney special adviser Beth Myers.

But she also took a swipe at the president's possible tactics. "We fully expect a 90-minute attack ad [by Obama] aimed at tearing down his opponent," she added.

Jennifer Psaki, Obama's campaign spokesman, said that the pressures of the day job, including the recent attacks on US embassies in the Middle East, had left the president little time to prepare. But Romney would come better prepared than any candidate in more than half a century, she said.

"The president will have some time to prepare, and he's been doing some studying but it is certainly less than we anticipated," she said. She even predicted that Romney could gain a boost in the polls from the debates.

The Obama camp has carved out time for three afternoons of preparations in Nevada starting today. In a mock debate, John Kerry, the 2004 presidential candidate, will play Romney.

"He'll have less time than we anticipated to sharpen and cut down his tendency to give long, substantive answers," added Miss Psaki.

That is, of course, one way of noting that the president has a tendency to be overly loquacious in answers.

It is all part of the psychological sparring. But the two campaigns know that on the big day, the debates remain the great wild card as the two candidates stand onstage.