IT IS Pavlovian. As soon as a president does something new in foreign policy, the world wants to know whether he has invented a new “doctrine”. The short answer in the case of Libya is that Barack Obama has not invented a new doctrine so much as repudiated an old one. What he is also doing, however, is challenging an American habit of mind.

The doctrine Mr Obama has repudiated is the one attributed to Colin Powell, the former chairman of the joint chiefs of staff and George W. Bush's transparently miserable secretary of state when America invaded Iraq in 2003. That held, among other things, that America ought to go to war only when its vital interests are threatened, when the exit strategy is clear, and when it can apply overwhelming force to ensure that its aims are achieved. Nothing could be more different from the account Mr Obama gave Americans on March 28th of his reasons for using military force in Libya. He does not believe that America's vital interests are at stake (though some “important” ones are); the exit strategy is not entirely clear (Colonel Qaddafi must go, but who knows when, and not as a direct result of American military action); and the force America is willing to apply (no boots on the ground) is strictly limited.

None of this should be a surprise. In “The Audacity of Hope”, the bestseller Mr Obama wrote as a senator in 2006, he set out a theory of military intervention. Like all sovereign nations, he argued, America has the unilateral right to defend itself from attack, and to take unilateral military action to eliminate an imminent threat. But beyond matters of clear self-defence, it would “almost always” be in its interest to use force multilaterally. This would not mean giving the UN Security Council a veto over its actions, or rounding up Britain and Togo and doing as it pleased. It would mean following the example of the first President Bush in the first Gulf war—“engaging in the hard diplomatic work of obtaining most of the world's support for our actions”.

The virtue of such an approach was that America had much to gain in a world that lived by rules. By upholding such rules itself, it could encourage others to do so too. A multilateral approach would also lighten America's burden at times of war. This might be “a bit of an illusion”, given the modest power of most American allies. But in many future conflicts the military operation was likely to cost less than the aftermath: training police, switching the lights back on, building democracy and so forth.

The president, it now emerges, remembers exactly what he wrote. He hesitated about whether to act in Libya (just ask the French and British, who egged him on but came close to losing hope), but he was always clear about how. All the conditions he wished for in that book five years ago have come to pass. In this week's speech he ticked them methodically off: “an international mandate for action, a broad coalition prepared to join us, the support of Arab countries, and a plea for help from the Libyan people themselves. We also had the ability to stop Qaddafi's forces in their tracks without putting American troops on the ground.” Under such circumstances, he said, for America to turn a blind eye to the fate of Benghazi would have been “a betrayal of who we are”.

Why does this theory of intervention, and the noble sentiment attached to it, fail to qualify as a “doctrine”? Because it is too elastic to provide a guide to future action. Would America “betray” itself by turning a blind eye to atrocities under different, less favourable, circumstances? So it seems. It has, after all, done so before, in Rwanda and Darfur—and Mr Obama appears to accept that it might have to do so again when, say, an alliance would be damaged, as in Bahrain, or the job is too hot to handle, as in Syria or Iran. Also unclear is whether an American interest must also be at stake before Mr Obama invokes the moral case for action. Conveniently (for the purpose of selling this particular war), the president detects a “strategic interest” in preventing Colonel Qaddafi from chilling the wider Arab spring, so nobody knows.

In fairness, elasticity is not a sin; and Mr Obama does not claim to have invented anything he calls a “doctrine”. The worst you can say about his approach is that it is merely commonsensical: decide the issues case-by-case while holding some idea of values and interests in mind. Many who say they want more consistency than this (typically by asking some variant of “What about Zimbabwe?”) do so not because they really believe that foreign policy can be run by an algorithm but in order to embarrass Mr Obama in any way they can. Prize chump in the case of Libya this past fortnight has been Newt Gingrich, the Republican presidential hopeful who demanded consistency, called for intervention and turned on a dime the instant Mr Obama answered.

After you, Sarko

More significant, however, is that habit of mind. In Libya Mr Obama is challenging the assumption of global leadership America has taken for granted ever since the second world war. America has joined coalitions before, but never under a president quite so adamant that America is not in charge—even if the military burden-sharing is indeed a bit of an illusion.

Most Republicans and quite a few Democrats hate this. Mr Obama's hope is that America's low profile will make the war more palatable not only to the Muslim world but also to the economy-fixated voters at home who question whether America can still afford to play its traditional leadership role. What he may soon discover is that modesty extracts a price of its own. By sharing the leadership with others, he has made his policy hostage to the limited mandate (no use of force for regime change) imposed by the United Nations and the limited means of his allies in Europe and the Middle East. It may not be a doctrine, it should not be a surprise, but nobody can deny that it is a gamble.





Economist.com/blogs/lexington