John Kerry threw caution to the wind last night as he launched a series of lacerating attacks on every aspect of the Bush presidency, accusing his opponent of failing American ideals both at home and abroad.

In by far the most biting critique of the campaign so far, Mr Kerry faulted President Bush for crippling American credibility, endangering American troops, fighting the wrong war on terror and misusing the Stars and Stripes before questioning his flaunting of God.

"As president, I will restore trust and credibility to the White House," he told a heaving convention centre of whooping, placard-waving delegates.

On the biggest night of his life, Mr Kerry cast off the careful approach which has exasperated some Democrats, and in doing so, as hundreds of red, white and blue balloons fell from the rafters, gave his party a scent of the White House.

Striking a populist tone, he used his speech accepting the Democratic presidential nomination to parade his credentials as a Vietnam veteran, running the theme of his military service throughout the 50-minute address.

He vowed to be a decisive commander-in-chief, insisting he would not shrink from using un-compromising and unilateral force to defend America. And with national security shaping the campaign battlefield, he warned European allies not to expect a dove in the White House if he wins in November.

"I defended this country as a young man and I will defend it as president. Let there be no mistake: I will never hesitate to use force when it is required. Any attack will be met with a swift and certain response. I will never give any nation or international institution a veto over our national security. And I will build a stronger American military."

Mr Kerry used the Iraq war as both the heart of his attacks against Mr Bush and also the backdrop to refer to his combat experience. Suggesting Mr Bush had been found out for being too simplistic, he said: "Some issues just aren't all that simple. Saying there are weapons of mass destruction in Iraq doesn't make it so. Saying we can fight a war on the cheap doesn't make it so. And proclaiming 'mission accomplished' certainly doesn't make it so."

He continued: "As president, I will ask hard questions and demand hard evidence. And as president, I will bring back this nation's time-honoured tradition: the United States of America never goes to war because we want to, we only go to war because we have to.

"I know what kids go through when they are carrying an M-16 in a dangerous place and they can't tell friend from foe. I know what they go through when they're out on patrol at night and they don't know what's coming around the next bend. I know what it's like to write letters home telling your family that everything's all right when you're not sure that's true.

"As President, I will wage this war with the lessons I learned in war. Before you go to battle, you have to be able to look a parent in the eye and truthfully say, 'I tried everything possible to avoid sending your son or daughter into harm's way. But we had no choice. We had to protect the

American people, fundamental American values from a threat that was real and imminent'. So lesson one, this is the only justification for going to war.

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