I meant only one accent spoken through the USA.
I don't think that's possible with a nation the size of the United States. Even with a very strong mass media, regional deviations in language are actually increasing throughout the nation. (see, "Introduction" Parnell, Thomas and Salmons, Joseph
Wisconsin Talks: Linguistic Diversity in the Badger State [Madison, University of Wisconsin Press], 2013) Also, in nation's that have a centralized educational system, you still can see remarkable diversity of dialects and accents. Case in point, the French someone speaks in Normandy is going to be different than that spoken in Paris or Provence; and France actually has a central language institute which is meant to formalize and standardize language. You can also look at the great regional diversity in nations such as Germany or Italy. Note that these countries are generally more centralized than the United States and also smaller in population and geography.
I'm pretty sure that having the same accent spoken as the vernacular throughout the United States is, if not ASB, than just a few inches to the left of our nearest resident Spacebat.