What is the US dog?

I am not aware of a national dog which represents all of the USA. The most popular dog for the last several years -- according to American Kennel Club registrations -- has been the Labrador Retriever. Also, the American Pit Bull Terrier has been used extensively in old war posters from the early 1900s, representing the "neutral but unafraid" America. But officially, I don't think America has a national dog per se.