Without a ground invasion, it would be difficult if not impossible to overthrow the current government

  The sudden act of western aggression is most likely due to fear that the rebels would soon be overrun. Its difficult to remove Gaddafi relying simply on rebel forces alone. They simply dont have the support and manpower needed for it. The man has no legitimacy when he has been effectively removed by his own people. Western aggression hardly makes that act of rebellion appear genuine. Thus aggression in the form of missile and air strikes is simply not enough. There needs to be some kind of physical force on the ground to remove him. But obama is already unpopular. His domestic policies are a failure and his foreign policies have no support except from the usual suspects. Thus the result is just blind aggression but far too limited to produce results.