An aggressive Republican fight back to defend Sarah Palin, the controversial Republican vice-presidential nominee, has been launched on the eve of her hugely anticipated speech to John McCain's nominating convention in Minnesota tonight.

After a day in which the Republican convention in St Paul had been blown off course by the Gulf coast's Hurricane Gustav and the daily revelations about Mrs Palin's personal and political past - including Monday's admission that her teenage daughter is pregnant - speakers led by President Bush rallied behind her and got down to the business of attacking Barack Obama.

The closing of ranks behind Mrs Palin, the 44-year-old governor of Alaska whose choice as John McCain's running mate has triggered accusations that she is an unvetted, inexperienced wild card, came amid signs that she might well weather the storm triggered by her nomination - barring any major new revelations from her home state in Alaska.

The fight back began with a short, nine-minute speech by President Bush delivered from the White House, in which he lavished praise on Mr McCain - whom he defeated in a bitterly contested 2000 Republican primary - as a courageous man "ready to lead this nation."

Mr Bush had been due to appear in person at the convention on Monday night until Hurricane Gustav intervened. His truncated video-linked address was a welcome compromise for the McCain campaign to distance the candidate from an unpopular president, without appearing to insult him. Although his approval rating is below 30 per cent nationally, the president is still popular with the Republican party faithful.

Mr Bush said: "When he takes office next January, John will have an outstanding leader at his side. America will have a strong and principled vice-president in the governor of the great state of Alaska, Sarah Palin."

Despite claims that Mrs Palin was the result of a hurried and flawed vetting process, and with many Republicans particularly nervous about an Alaskan ethics investigation, the choice of Mrs Palin, a pro-life, fiscal and social conservative, has electrified the Republican base, with senior aides to Mr McCain believing that media attacks on a mother-of-five with a compelling life story could well backfire.

Leading the counter-attack was Fred Thompson, the former Law & Order star who briefly campaigned for the Republican nomination last year.

In a performance that earned several standing ovations - not least from his attacks on Mr Obama - Mr Thompson described Mrs Plain as a "breath of fresh air." He added: "She is from a small town, with small town values, but that's not good enough for those folks who are attacking her and her family."

Decrying the Washington "big shots" and its "cocktail circuit", he said: "Give me a tough Alaskan governor who has taken on the political establishment...and won - over the business as usual crowd any day of the week." He said Mr McCain's decision to place her on the ticket "has the other side and their friends in the media in a state of panic."

Turning his attention on Mr Obama, and to a thunderous ovation, Mr Thompson described the Democratic nominee as the most liberal, most inexperienced nominee to ever run for president.”

In a reference to Mr Obama’s recent speech to 200,000 in Berlin, Mr Thompson compared the two nominees to paint the Democrat as bolstering anti-American sentiment abroad.

“The respect he is given around the world is not because of a teleprompter speech designed to appeal to American critics abroad, but because of decades of clearly demonstrated character and statesmanship,” he said of Mr McCain.

Conservatives, slow to warm to McCain even after he clinched the nomination in February, were particularly supportive of Mrs Palin.

"I haven't seen anything that comes out about her that in any way troubles me or shakes my confidence in her," said former Arkansas Governor Mike Huckabee, who ran unsuccessfully for the party's presidential nomination this year.

"All it has done for me is say she is a human person with a real family."

Ron Nehring, chairman of the California state party, said video footage of Palin on a firing range was helping her cause.

"The reports I'm getting back is that every time they show that footage we get 1,000 precinct walkers from the NRA [National Rifle Association]" he told members of his state's delegation, to laughter. "She cuts taxes and shoots moose. That's Governor Palin."

The most intriguing speaker of the night was Joe Lieberman, Al Gore's 2000 running mate, who has effectively defected from his party over the issue of Iraq. A man who Mr McCain had dearly wanted to be his vice-presidential pick - his liberal social views would have triggered a grass roots revolt - said: "What is a Democrat like me doing at a Republican convention like this? The answer is simple. I'm here to support John McCain because country matters more than party."

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