So it was with Margaret Thatcher and Ronald Reagan as well as Tony Blair and George Bush. But when it comes to Libya, the tables seem to have turned. For the clearest explanation of the war aims has emanated not from Britain, or indeed Europe, but the White House. While Britain has blundered (William Hague suggested at one point that Muammar Gaddafi had fled to Venezuela) and Nicolas Sarkozy has blustered (starting the bombing without telling his allies), Barack Obama has offered the most lucid justification for military intervention.
The trouble is that at each moment the goals of the intervention not only changes, but also contradict any justification given earlier. Shortly before the no-fly zone was imposed, Obama assured a bipartisan group in Congress that the action would take "days not weeks". More than a week after the bombing had started he told the nation the aim was limited to purely humanitarian ends. "I refuse to wait for the images of slaughter and mass graves before taking action," he said.
He also stood steadfastly against regime change. "If we tried to overthrow Gaddafi by force, our coalition would splinter." Two weeks later, in a joint letter signed by David Cameron and Sarkozy, he brazenly conceded it is about regime change. "It is impossible to imagine a future for Libya with Gaddafi in power."
Assassination is now, apparently, the foreign policy du jour. On Sunday, the British defence secretary, Liam Fox, insisted: "Nato does not target individuals." Instead they go for families. Just over a week ago, they killed Gaddafi's son and three of his grandchildren.
So here we are with a conflict that was supposed to last days and was not about regime change that has gone on for six weeks and won't end until the regime has changed. Even as the west prepares to negotiate a truce with the Taliban, Gaddafi's offer of a ceasefire has been rejected summarily. In the name of humanitarianism, the war must be prolonged.
The problem is not mission creep, it's the mission. There are only so many times their governments can reasonably keep doing the same thing and expect different results and there can be only so many times liberal hawks can "trust" their governments to do differently.
Despite Obama's initial foreboding, Libya is not Iraq. It came with legal sanction, European insistence, Arab cover, a credible, if not exactly viable, resistance on the ground, and the immediate threat of massacre. Iraq had none of those.
UN support makes the bombing legal, it does not make it legitimate. This is no mere semantic matter. Just because something is within the law does not make it a good idea. International law should be a prerequisite for action, not the basis for it. The Iraq war would still have been a disaster even if the UN had endorsed it. It would just have been a legal disaster.
The international support also changes the character of the war. Americans do not have a monopoly on arrogance or hubris. It was the French who led the charge to war.
"The historian of domestic politics treats the explosions of war as if they were offstage disturbances," writes Walter Karp in The Politics of War. "Were that true, we would have to believe that presidents who faced a mounting sea of troubles at home have nonetheless conducted their foreign policy without the slightest regard for those troubles ... that individual presidents were divided into watertight compartments, one labelled 'domestic' and the other 'foreign'." In Sarkozy's case, the bombing started the day before his party received a drubbing in local polls with his approval ratings hovering around 30% and the Front National threatening to eclipse him. As he spearheaded a bid to control internal EU migration shortly after, it was also telling that the very Libyans he was so desperate to save he was also desperate not to provide sanctuary for if and when they fled.
Britain was also gung ho. But it rapidly became apparent, as they both begged the US to step up its involvement, that they started a fight they could not finish.
One of the more pathetic aspects of this misadventure is how it has exposed the discrepancy between their imperialist rhetoric and postcolonial decline. Obama hoped the US would play a "supporting role"; in reality it is centre stage. Indeed the show could not go on without Washington. However, even at this early stage, American domestic support for this war is fragile. Most believe the US should not be involved and that it does not have a clear strategy – and, in any case, they are not that interested. This is not a question of the ends justifying the means. As both Iraq and Afghanistan have shown, the west does not have the military or political means to achieve its ends even on its own terms.
The Libyan rebels' demands are important. But solidarity does not involve unquestioningly forfeiting responsibility for one's own actions to another, but rather it is a process of mutual engagement demanding an assessment of what is both prudent and possible. It is now clear that the Libyan uprising, like other revolutions in the region, could not succeed militarily.
The argument that a massacre was truly imminent is the strongest – even if those who sold Gaddafi the weapons he would use to carry out that massacre are in the weakest position to make it. We will never know how accurate that prediction was because the no-fly zone was imposed. To some that may be justification enough. But the same can be said for Syria and Yemen, where the state has turned against the protesters, many have died and protests continue. And there the international community has proceeded with a combination of sanctions and diplomatic isolation.
Revolutions and civil wars have no guarantees of a happy ending, and foreign intervention is rarely the answer. We've seen from elsewhere that the most successful way to build democracy in the region is by ordinary, local people from below, not by foreign precision bombs from 50,000 feet above.
Either way, what was clear from the outset was that such an intervention was not sustainable without regime change and then occupation. The mission had to creep, because as it stood it wasn't going anywhere.
Sometimes there are no good answers. But that doesn't mean war should be the default position. Because some answers are worse than others. And this is shaping up to be predictably bad.
As a US senator said in New Hampshire when asked whether he would leave troops in Iraq to prevent genocide: "Well, look, if that's the criteria by which we are making decisions on the deployment of US forces, then by that argument you would have 300,000 troops in the Congo right now, where millions have been slaughtered as a consequence of ethnic strife, which we haven't done. We would be deploying unilaterally and occupying the Sudan which we haven't done."
His name? Barack Obama.