Regime change is what the coalition flying sorties over Libya wants. If that wasn't obvious enough already, a senior European diplomat Wednesday made it explicit to me: "It's been crystal-clear from the beginning: Gaddafi must go."

But what's the strategy? The U.N. resolution under which the coalition operates only authorizes the protection of civilians, and no one wants to deploy ground forces. To oust Gaddafi, won't the coalition need to violate the terms of the U.N. resolution or its own determination not to use ground troops?

Actually, the coalition is making a bet, the diplomat explained, that it will be able to accomplish regime change without doing either.

The U.N. has commanded Gaddafi to vacate his forces from cities across Libya. The dictator hasn’t complied, giving the coalition reason to step up its mission, to "destroy his tanks" and "weaken his regime more and more." After all, the diplomat said, the U.N. resolution gives the coalition permission to use all necessary means to enforce it.  

The U.N.'s are "demands that Gaddafi cannot comply with," the diplomat explained. The dictator is "in the spirit of a war," he continued. "It seems difficult for him to withdraw his troops, to retreat to a small neighborhood in Tripoli."

"We think that, for Gaddafi, it is black-and-white."

As long as the dictator sees it that way, coalition strikes can continue with the U.N.'s blessing.

This strategy relies not only on a reading of Gaddafi's psychology, but also on "an opposition who want to fight for a united country," the diplomat explained, since someone on the ground will have to press Gaddafi's steadily weakening forces directly. He expressed confidence that the Benghazi-based opposition — "articulate people in favor of a democratic transition" — was committed to the Libya's unity, not settling for a long-term Kurdistanization of the east under the protection of coalition air power.

The strategy could work. But there are risks.

What if Gaddafi, battered by air strikes, complies with U.N. demands? The coalition could easily fracture over how much more it should do, or whether it would even be worth keeping military assets devoted to Libya in case Gaddafi changed his mind. Policymakers should think now about what they would do.

Barring that, will the opposition have the wherewithal to topple Gaddafi, even with coalition command of the skies? The coalition could make that more likely if it began arming and training the rebels, too.

Then there is the question of what happens if the coalition’s strategy succeeds. If the opposition wins, how much will the coalition need to intercede in the political transition it enabled? The diplomat seemed optimistic about the emerging rebel government. But it's impossible to know how long it will really take to win the peace.