Nato and Libya: What now?
Nato's aim in the Libyan conflict is on the face of it crystal clear - to enforce UN Security Council resolutions calling for the protection of civilians in Libya.
It is not, the US President Barack Obama, his French counterpart, Nicholas Sarkozy, and British Prime Minister David Cameron, tell us in a joint newspaper article, "to remove Gaddafi by force".
But as time goes on - as the Libyan government's military shows no sign of collapsing or pulling back from besieged towns like Misrata, and the Libyan rebels show little ability to defeat their opponents - things become a little more complicated.
From the outset of the fighting there have been repeated calls for Col Muammar Gaddafi to step down.
Now the three Nato leaders say in their article: "So long as Gaddafi is in power, Nato and its coalition partners must maintain their operations."
So their message is clear - this conflict can only end in one way, Col Gaddafi must go and the Nato mission will continue until he does.
But they must then confront the military reality on the ground. Neither side is winning. There are fears that Nato air power alone cannot secure a decisive outcome.
The danger is a stalemate that could last for many more weeks, if not months.
This inevitably is a problem for Nato.
The alliance only picked up command of the mission once it was under way.
Indeed, this was a peculiar operation from the outset, since it was two European countries - Britain and France - who were in pole position with a reluctant Washington only assuming initial command after a good deal of hesitation.
Subsequently the Americans moved to take a back seat. Nato assumed command and the Europeans were expected to pick up the slack.
Since then, only six Nato countries, five of them European - Britain, France, Belgium, Denmark and Norway, along with Canada - have actually been conducting ground strikes against Libyan forces.
Others have either been reluctant about the operation from the outset or have particular historical reasons, like Italy, for not wanting to drop bombs on Libyan soil.
Nato's Secretary General Anders Fogh Rasmussen noted on Thursday that the alliance had been short of strike aircraft.
This has caused considerable frustration in Paris and London. Nato may be carrying out its military duties efficiently - it generally does - but the alliance is much more than just a conductor of the military orchestra.
It is above all a diplomatic body providing the political will, rationale and determination to conduct a given operation.
And in the Libya crisis - on all three fronts - Nato's members have been found wanting.
Arming the rebels
Where Nato's planes come from, at one level, does not matter, but in another sense it is fundamental, since burden-sharing of risks and responsibilities should be what the alliance is all about.
Part of this past week's diplomacy, with meetings of the "contact group" on Libya in Qatar and Nato foreign ministers in Berlin, was to bolster the coalition for the long haul.
One phase of this conflict is over, and perhaps the crucial phase is about to begin.
Nobody knows how long it will last and that is why a whole raft of other options are now being seriously considered, such as arming the rebels - something Qatar, for one, appears eager to do.
UN Security Council resolution 1973 rules out "occupation" of Libya by foreign forces. Might it allow for some limited operation on the ground, say with a robust humanitarian purpose? That is one for the legal experts to argue.
But it is instructive that the French at least seem to be raising the possibility of something that appeared unthinkable just a few weeks ago - the prospect of Nato boots on the ground.
Such a decision could be crucial for Libya's future, but it will also be important for that of the Atlantic alliance itself.