Well, he's already making his first forays into Benghazi, combined with some shelling. I think it's going to take some significant pounding from the West to keep him out, and if he gets in then there's a real problem.
I gotta say, if Obama manages to pull of the sort of maneuver he's shooting for, I'll be fairly impressed. All indications are that he's looking for the US's involvement to be a very strong support role while the rest of NATO does the heavy lifting. This could be a very good strategy. We have a lot of unique capabilities and anybody can drop bombs on ground forces. If we provide quality battlefield reconnaissance and electronic warfare support, the Brits, French and token Arabs can really whip some ass against Gadaffi's armor. Plus, it doesn't put us solely at the head of the policy decisions. He's trying to make this much more like Bosnia than Iraq and that's a good call.
The policy decisions are a sticky wicket. Aside from trying to prevent wholesale slaughter in Benghazi, I'm really not sure what the objective should be here. There is no mandate for NATO to take out Moammar, but I don't see how you just leave him there in charge of 85% of Libya.