Dawidoff suggests that Frank is the most influential photographer living today, and that would be hard to argue against.
This brings back memories, years ago, of the first time I visited S. D. in her small Los Angeles studio, and saw affixed to her bulletin board, a postcard from Robert Frank.
Find a copy of “The Americans” if you can, and study it, remembering that it dates back to 1958. Or at least look at the NYT special feature on the book here.