What wild bird did I see?

I live in the mid-Atlantic United States (nowhere near any saltwater), and I saw a bird yesterday I could not figure out despite referencing our Sibley Guide to Birds and its awesome illustrations. The bird was circling over the highway like a hawk, eagle, or vulture does when looking for food. The body and wings were all entirely dark brown/black. The head was white, and the tail was white and a fanned-out shape. The bird was not the size of an eagle, more like an oversized gull, but the coloration and wide wing shape are definitely more in line with a vulture/eagle/hawk. Honestly, it looked like a bald eagle, but it was too small to be one.

Any ideas?