You don't see Barack Obama look hesitant very often.

But watching his news conference with German Chancellor Angela Merkel, I saw a hint of it.

He was in Baden-Baden before NATO's 60th anniversary summit began.

The Obama effect had worked its magic on thousands of teenagers over the border in the French city of Strasbourg.

And he did a lot to repair ties between the US and Europe that suffered under the previous administration's go-it-alone tendencies, which had put so many noses out of joint on this side of the pond.

He needs NATO countries here in Europe onside if he's going to persuade more of them to join the fight against the Taliban insurgency in southern Afghanistan.

But asked about the NATO mission there, Obama started to drift a bit, telling reporters that military action alone won't solve a country the US and its allies are losing control of.

What he meant was that the strategy for Afghanistan needs to focus more on winning civilian hearts and minds by investing in schools and hospitals as well as creating an army and police force capable of protecting their own.

If that sounds familiar, then that's largely what the US and its allies did in Iraq on top of installing a new, democratic regime.

But Afghanistan is a test case for NATO - its first mission outside Europe - and there's concern about what exactly its role is.

Remember, NATO evolved in a time when we used phrases like Iron Curtain and - in the UK, at least - the government encouraged you to dig a bunker in your back garden so you could take cover when World War Three broke out.

It was an alliance against the Soviet Union, with the mantra "an attack on one is an attack on all of us".

That still stands, but that was pretty much its raison d'etre during the 1950s and 1960s - NATO didn't have to think about the aftermath and making sure its enemies had running water.

Obama said the NATO mission wasn't about occupying or running Afghanistan, but will it have the luxury to confine itself to toppling the Taliban?

With bombings and attacks now almost routine in Kabul, the Afghan government can't pretend to be in control.

So would NATO somehow have to govern instead? It's not clear because the alliance is in unchartered territory right now.

Obama wants to destroy al Qaeda - an organisation that's proved itself adept at shifting across countries and continents.

Potentially, we're talking about NATO forces chasing insurgents across the world as a global policeman.

That's an awfully big challenge for an organisation struggling to get extra troops to finish its current war in Afghanistan - and one the leaders gathering in Strasbourg this weekend might prefer to avoid talking about for fear of spoiling the birthday party.