US President George W. Bush insisted on Thursday he had no advance warning of the September 11, 2001 attacks and challenged the assertions of a former aide who accused him of not placing a high enough priority on pursuing al Qaeda prior to the tragedy.
Visiting a community college in the election swing state of New Hampshire, Bush tried to shore up his credibility on national security, which may be key to stopping Democrat John Kerry from taking the White House from him in November.
"Had I known that the enemy was going to use airplanes to strike America, to attack us, I would have used every resource, every asset, every power of the government, to protect the American people," Bush said, appearing with Cheryl McGinnis, the wife of a pilot killed in the attacks.
Counter-terrorism expert Richard Clarke, who served the last four US presidents, said Bush did not take the threat of Osama bin Laden's al Qaeda organisation seriously and downgraded its importance in comparison to the administration of former President Bill Clinton.
Clarke gave his scathing critique of Bush in testimony on Wednesday before the commission investigating the events leading up to the September 11 attacks on the World Trade Centre and the Pentagon.
One of the most damaging revelations was a letter Clarke wrote a week before the attacks asking White House policymakers to imagine a day after hundreds of Americans lay dead at home and abroad after a terrorist attack and ask themselves what they could have done.
One grass-roots organisation has already rushed out anti-Bush television ads highlighting Clarke's testimony.
BUSH RAISING MONEY ON KERRY TURF: The White House has sought to undermine Clarke's credibility, brandishing comments he made previously which had been favourable to the administration.
Clarke's allegations, detailed in a new book, have blanketed the airwaves, putting Bush on the defensive just as his campaign had moved into a new aggressive phase with ads assailing Kerry.
As Clarke spoke out, Kerry stayed out of the fray on vacation. He returned to the campaign trail on Thursday, promising to restore trust in the White House.
Bush later on Thursday raised $1.2 million in Kerry's hometown of Boston. At the New Hampshire event, he had planned to discuss the economy but digressed to defend his leadership on security.
The president did not mention Clarke, but did refer to the September 11 commission, with which his administration has had a somewhat rocky relationship.
Bush praised the panel for doing "very important" work and noted it was looking not only at his administration's actions ahead of the attacks but also "the eight years of the previous administration."
Bush initially opposed the commission's creation and at times in the past few months has been involved in delicate negotiations over the timing and circumstances of his own testimony and those of his staff.
The president agreed to meet with the commission but both he and White House national security adviser Condoleezza Rice have declined to testify in public hearings.