At the climax of Harper Lee's "To Kill a Mockingbird", set in the early 1930s, Atticus Finch equates a "stupid man" to "an Einstein" in order to emphasize to the jury, in his closing arguments, the impartiality of an American court of law. How well would this comparison have been taken by the jury and the spectating public? Today, calling somebody "Einstein" is synonymous with "genius". I had always assumed that Einstein gained widespread national recognition in the US for his work on the atomic bomb. Was Einstein already a well-known public figure by then?
See my long answer in this thread. The short answer is: after the Eddington eclipse expedition of 1919, in which "Einstein overturned Newton" in the popular mind, Einstein began his ascent into "genius" in the popular imagination. This was further reinforced after the invention of the atomic bomb, which was linked in the popular mind with E=mc^2, and certainly by 1960, when Lee published the book, he would have been. (Whether he would have been the one a defense lawyer in the American South would have cited in the mid-1930s, I don't know. It's not impossible; by 1938 Einstein had been on the cover of Time magazine twice. If one were merely trying to conjure up "genius" there are probably more reliably — and perhaps less politically fraught — names that might have been dropped in 1936 or so, when the book is set.) Keep in mind that there is a wide gap between "popular perceptions of who the best scientists are" and the views that scientists themselves have (either at the time or after the fact).