It is a bit ridiculous, isn't it? It seems that our speedometer in Km must be changed to one in those strange miles that only the USA uses any more. Oh, the right hand mirror must have those words etched upon it; of course you read them every time you use that mirror, right?
You CAN drive your foreign Smart in the USA, just as we do when we visit. It is registered in Jalisco and we buy a temporary liability policy for the time we are in the USA. You CANNOT permanently import it or register it in the USA without jumping through hoops.