Writing about fellow author Jack London, "J.L.", and Sinclair’s book "The Cup of Fury," which includes a discussion of Jack London, Sinclair writes, "To the public he [London] is a romantic figure & has to be that to sell the book. But to me he is an alcoholic tragedy. I have made him a leading figure in ‘The Cup of Fury’...." Sinclair discusses the book, saying, "A score of NY publishers said it wouldn’t sell & I had to go to a church group. They have sold 65000 copies... I send you my ‘Didymus’ of which also US publishers are afraid. It has been published with success in London, Paris...." He signs, “U. Sinclair.” "The Cup of Fury" was published in 1956; it is an attack on alcohol, the tragic stories of talented American writers whose drinking destroyed them and caused grief to others, people like Jack London, O. Henry, Sinclair Lewis, Edna St. Vincent Millay, and Dylan Thomas. Sinclair also refers to another book, "Didymus." He is talking about the book "What Didymus Did," published in the UK in 1954, which would, in 1958, be published in the US as "It Happened to Didymus."
In 1919, he published the muckraking exposé about "yellow" journalism, "The Brass Check," revealing the limitations of the “free press” in the United States. Four years later, the first code of ethics for journalists was created. Sinclair also ran unsuccessfully for Congress as a Socialist, and was the Democratic Party nominee for Governor of California in 1934.