George Bush has insisted repeatedly on the campaign trail that his presidency has been characterized by unwavering policies based on core convictions. But a key component of his security and military strategy -- a willingness to wage war "pre-emptively" against perceived enemies -- lies largely in tatters, say experts and policy-makers.

These experts, from both sides of the political spectrum, say the brutal experience in Iraq has eroded many elements of what has come to be called the "Bush doctrine," leaving the United States with less flexibility in the war on terror.

President Bush himself appeared to dial back on the doctrine during Thursday night's debate when asked whether he would launch future pre-emptive strikes in the wake of the Iraq war. Bush replied, somewhat unenthusiastically, that "a president must always be willing to use troops," but only "as a last resort."

That is a far cry from the bold policy the president articulated in 2002, which rejected the traditional focus on containing threats or responding only after an enemy had staged a clear act of aggression.

In fact, say policy experts, the violent insurgency in Iraq, which has tied down 140,000 U.S. troops, has all but removed Americans' stomach for a similar pre-emptive engagement against an enemy who has not actually launched or prepared an imminent attack on the United States.

Iraq "will leave a long and damaging legacy," said Fred Ikle, a senior government arms control expert for decades who has argued that the United States must be more willing to use military might to achieve its goals. "It will inhibit us more than is good for our future. We fumbled."

Ikle was one of the founders of the Project for the New American Century, a neoconservative group that has long pressed for a more muscular American military posture, and includes Defense Secretary Donald Rumsfeld and Deputy Defense Secretary Paul Wolfowitz -- key architects of the Iraq war -- among its members.

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The Bush administration continues to insist that the doctrine remains U.S. policy. It has a number of elements, including an insistence that any state that supports terrorists will be considered an enemy, that the United States has the right to attack such countries pre-emptively -- even, as in the case of Iraq, before an enemy has mounted a challenge or the president feels there is an imminent threat of an attack.

Under the doctrine, the United States would also act to prevent any country from even attempting to match American military might.

Most of these elements were outlined in speeches in 2002 and then codified in September 2002, in a 33-page document called "The National Security Strategy of the United States." It stated that terrorism presented a new kind of danger and needed a new kind of response.

"As a matter of common sense and self-defense, America will act against such emerging threats before they are fully formed," the document said.

Bush went further and targeted three countries in his famous "axis of evil" State of the Union speech in 2002, hinting that Iran and North Korea, as well as Iraq, might be attacked pre-emptively if they were perceived as threatening the United States.

But many experts say that the first broad pre-emptive invasion might be the last, at least for now, because of the expense of Iraq, the apparently poor planning for the occupation, the violent backlash and the lack of resources or troops for another such venture.

Rather than be cowed by President Bush's earlier hints, or by the U.S. invasion of Iraq, both Iran and North Korea have defied international demands, and both appear to be developing nuclear weapons, without any indication that the president might seek to resort to a pre-emptive attack. In the presidential debate Thursday night, President Bush emphasized multilateral talks, involving China, to resolve the North Korea crisis, and Bush has looked primarily to European negotiators to deal with Iran. (San Francisco Chronicle)