Fine words?

So Obama, Cameron and Sarkozy are putting their backs to the wheel? The Independent reports:

Barack Obama, David Cameron and Nicolas Sarkozy have stated their determination to keep bombing Libya until Muammar Gaddafi steps down or is deposed. The leaders of the United States, Britain and France said, in a jointly written article, it would be an "unconscionable betrayal" of the populations of rebel towns to cease operations with Colonel Gaddafi still in place. It was "unthinkable" that a leader who has "tried to massacre his own people" could be allowed to continue in government, they said.

Sounds good. But what if bombing Gaddafi does not achieve the desired end of removing him from power? After three weeks of bombing, we are no nearer to regime change; indeed, if anything, the Gaddafi regime has become stronger. At what stage do the allies walk away, saying that at least they gave it a good try? Impossible? But if the only viable alternative is US, British and French boots on the ground ...